To begin, let's recognize that ALL HDD's are just a type of device, and any Windows needs a device driver to use any device. Narrowing down, Win XP needs a driver to use IDE devices, and another driver to use SATA devices, and many others for other devices in your system. Now it happens that, since IDE had been around for so long, Win XP has an IDE device driver "built in", along with a few others like ones for floppy drives and basic VGA graphics hardware, etc. But it does not have a built-in driver for SATA devices (or, more properly, AHCI devices), so the first time such a device is added to your system, Windows likely will go through its usual routine - it will detect the presence of a new device type, let you know, then look for and install a driver for it from its files on your existing HDD. If it cannot find that driver, it will ask you where you want it to look. So, to add a SATA HDD to your machine running Win XP in ANY version, you would have to add the SATA or AHCI device driver. But there's a work-around you have probably used, so read on.
The real "problem" comes if you want to use a SATA HDD as your boot drive that you install your Win XP onto. Win XP does not know how to use a SATA device, so it cannot boot from one. Hence, the Win XP Install routine will not detect, and will not install to, a SATA drive. Well, that's a big issue considering that XP and SATA arrived on the scene at nearly the same time! Windows has, for a long time, had a way to handle this, though. Early in the Install process you get a screen that asks whether you want to install any extra device drivers (that is, additional to the "built-in" ones) - if so, you must press the F6 key. If you don't, a timed wait occurs and then it proceeds onward. But if you press F6 here, you enter a routine that allows you to install any device driver you want to become a permanent "built-in" type of driver in this particular installation. This is how drivers for SCSI, RAID, and now SATA devices can become part of your custom Win XP. The dilemma is that Win XP only knows how to load those drivers from a floppy drive! So, to make this work, you have to have a floppy drive in your machine (even if only temporarily) and a floppy diskette with the required driver already copied onto it. In fact, the routine will return to its starting point after installing one driver, and ask if you have any more to install. Only when you say no does it go back to the regular Install routine. When you do this, Win XP places copies of the drivers you just installed in a particular place on the HDD and loads them very early in every subsequent boot, so it can use those devices for everything - even to boot from.
NOTE that, if you plan to boot from an IDE device and then add and use a SATA device for data only, you do NOT need to install the AHCI or SATA driver as part of the initial installation of Win XP. It can be installed into a running Win XP later when the SATA HDD is added to the system. This works because Win XP boots and loads itself from the IDE device, and then reads from that device all the other drivers it needs - like USB port drivers, printer drivers, video drivers, sound chip drivers, etc., and including an AHCI driver.
But what about all those people with no floppy who want to install Win XP on a SATA drive? Well, BIOS makers and mobo manufacturers created a neat work-around for that. In most BIOS's these days, near where you Enable the SATA ports, there is a place where you can set the SATA Port Mode. Usually this has options like IDE (or PATA) Emulation, SATA, AHCI, and RAID. Setting this to SATA or AHCI is the "normal" way to use a true SATA HDD, but that requires the installation of the SATA or AHCI driver. Setting it to RAID would require installation of a RAID driver. But setting it to IDE (or PATA) Emulation has the BIOS intervene and treat the SATA device just like an IDE device, fooling Win XP into believing that's what it has. And Win XP knows all about IDE drives, so it's happy with NO additional drivers added. But this means that a few features of the new AHCI device will not be available because the BIOS will never allow them.
In your case, you originally installed Win XP on an IDE device. LATER you cloned that to a SATA HDD and disconnected the old IDE drive, and it still works just fine. I am sure, then, that you have your SATA Port Mode set to IDE Emulation so that the existing Win XP with NO additional SATA or AHCI device driver installed can still boot from this device - because the BIOS is hiding its true nature and making it behave exactly like an IDE drive.
Now, to the question of why the two drives don't get along. This should not be happening. I suggest you check the area of the BIOS where you specify the Boot Priority Sequence. Probably you will have to have both HDD's installed to do this. To enter BIOS Setup usually you must hold down the "Del" key while the boot is happening, until the first Setup screen appears. BUT watch your screen for a prompt about exactly which key gets you into BIOS Setup, in case it is not "Del". Now find the Boot Priority Sequence setting place. It will list your possible storage devices you could try to boot from. Many people have these set to try the optical drive first, then the HDD they want to boot from. In your case, just make sure that the HDD specified is the SATA new drive. And then make sure that the list does NOT allow it to try the old IDE drive. In other words, there should be only TWO choices - optical, then SATA, then NOTHING else. Once this is set, Save and Exit to boot.
If that does not solve it, check one other thing. Did you make any changes to jumpers on your drives? I expect that originally you had the old IDE drive as the Master device on one IDE port, possibly with a Slave device (maybe your optical drive?) on the same port. If you re-install the old IDE drive, it should still be set that way (Master) and any second device on that port and cable should be set to Slave. The fact that the HDD is not being used to boot from has NO impact on jumper settings! An IDE port MUST have one Master device and MAY have a Slave device also. On the other hand, for your new SATA HDD there is NO jumper to set. There is no such thing as Master and Slave on a SATA port - it only has ONE device on it. In fact, although there are jumpers on many SATA drives, they are used for other things entirely and should not be changed unless you really know what you're doing. The jumper settings for Master and Slave on IDE devices do NOT have anything to do with which device is the boot device - that is set separately in BIOS.