One question.

A friend has a computer he'll give me, but it runs win 98. If i just switch my HD and his HD, will everything work if i install the right drivers?

I think windows XP (haven't tried vista) kinda configures according to each pc, so I'm not sure if it's gonna work.
However, if you clean your HDD ( save on some other HDD or cds what is important for you) and then install everything while it is plugged on the other pc, there should be no problem.

Nah. I can't do that. I don't know where I put the CDs for XP.

Search bittorrent sites for a win xp intall cd, if you have your legal CDkey it will install and update no problem My old packard bell didnt come with a CD at all so I downloaded a XP SP2 CD used my key and it works everytime no problem i still use that same CD and have been for the last 2 years or so.

A fresh install would be best becasue the motherboards will be different and have different drivers etc and may conflict.

u could also do the windows 98 to xp and use your serial key.

Take the pc, and do what these others said find a version of xp on bittorrent. Reformat the drive in that pc and install xp, set it up and see if it works better than yours. If its running win 98, Id bet the specs are worse than what you have now. As far as what you asked if you could do, no dont do that. If it turns out the other pc is better than yours, you can always add your existing hdd into that machine as a slave after you have it running right and still have all your data on a secondary drive.