I have an HP Desktop as you all know. It has a Lite-On CD-RW drive in it. If I replace that with an NEC DVD+/-RW drive in it, will it cause anymore stress on my PSU or anything else?
Yeah, pop it in there and that's it. You MIGHT have to find some more software, espcailly if your drive is OEM and doesn't come with anything. Other than that, though, no drivers are typically needed
If you want to burn DVD's, you'll need software such as Nero, Roxio, DeepBurner, etc, because XP only has native burning support for CDs, not DVDs, as far as I am aware.
Tom