Adding RAM - combining stick sizes?

Hi guys, I just have a quick question...

My girlfriend's HP PC is in need of some upgrading. It came with only 1GB RAM and Vista 32. Before I met her she had some friend install a 1GB RAM stick, so now it has 2GB RAM but with 3 sticks so it's in single channel mode. I'd like to buy another 1GB stick for her so she'll have 3GB, but my question is can I get dual channel with this combo?

It would be 1GB+512mb per channel... I'm thinking it should work but just wondering if anyone has experience here?

EDIT: I've determined as well that the current CPU is a Core 2 Duo E4300 1.8ghz. I found that the list of compatible CPUs extends up to a Core 2 Duo E6x00 (Conroe) up to E6700, and I might be able to get an E6500 for $85 locally... the concern here is that the FSB of the E4300 is at 800, while the E6700 is 1066. I'm pretty sure her 512mb modules are only 533mhz (and they're Samsung brand lol), but the 1gb stick is a Kingston ValueRAM at 800mhz... There shouldn't be any issues having the 533mhz RAM and a 1066mhz CPU right? I can't edit anything in the BIOS, since it's an HP... I just have to hope it works.

Second Edit: E6500 doesn't have integrated graphics but it appears the P5LP-LE (Leonite) mobo does have GMA950 onboard graphics... so I don't need IGP on the CPU right?
 
Solution
I suggest you get the actual mobo model number and research what it can/can't support before you buy a CPU that may not work at all. The dual channel memory question is easier, if you can match the 1st 1GB DIMM or find 2 matched DIMMs you will be much more likely to get dual channel going. Last, you don't need IGP on the CPU with this family of GPUs (they don't support), rather the mobo chipset includes a GPU.

EDIT: Looks like you will be okay with the 6700. Here is the HP link describing the mobo:
http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&dlc=en&cc=us&docname=c00864946#N923

COLGeek

Cybernaut
Moderator
I suggest you get the actual mobo model number and research what it can/can't support before you buy a CPU that may not work at all. The dual channel memory question is easier, if you can match the 1st 1GB DIMM or find 2 matched DIMMs you will be much more likely to get dual channel going. Last, you don't need IGP on the CPU with this family of GPUs (they don't support), rather the mobo chipset includes a GPU.

EDIT: Looks like you will be okay with the 6700. Here is the HP link describing the mobo:
http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&dlc=en&cc=us&docname=c00864946#N923
 
Solution
One thing to keep in mind for running in dual channel you will want to have the same size modules in the same color slots (ie. the 2 512MB modules in the blue slots and the 2 1 gb. modules in the brown slots) since this is how the MOBO is designed to use them and it will not run dual channel if there are different size modules in a set.
 
As it turns out, we decided to go a slightly different route. Going to upgrade the mobo and CPU to an E5400 and Biostar G41 M7. We bought 4gb DDR2 800mhz CL5 RAM rather than upgrade just 1 gb stick.

Thanks again guys.

(although just to be clear, if we have slots 1 through 4, it would work with 1:1gb 2:512mb 3:1gb 4:512mb right? 1 and 3 being black, 2 and 4 being white)