Yes, the newer drives (and the cables) are backwards compatible, and will run at the older, lower bandwidth and speed settings. That would happen automatically with an ATA/66 or ATA/100 drive, simply by being on a regular 40 pin, 40 conductor cable.
The best thing you could do would be to purchase a relatively inexpensive ATA/100 controller card, and then connect the new drive. That will give you some upgrading ability, without having to change the mainboard, and the faster drive will give your system a nice performance boost.
The way I look at it ... if you are willing to consider the purchase of a larger, fast drive ... what's another $30-$35 dollars for a controller card? That will also give you another 4 IDE ports, which will allow for other, faster devices in the future.
Food for thought.
Toejam31
<font color=red>My Rig:</font color=red> <A HREF="http://www.anandtech.com/mysystemrig.html?rigid=6847" target="_new">http://www.anandtech.com/mysystemrig.html?rigid=6847</A>
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<font color=purple>"Have you noticed how much they look like orchids? Lovely!"</font color=purple>