I did something similar a couple computers ago...had two computers running 98, put the hard drive of one into the other. My solution to this was to do a straight reinstall of windows 98 onto the new drive, and just delete the windows folder off the original drive. I'm not sure how well it would work for XP, though.

Anyway my best advice would be to make an attempt at really cleaning off the gateway drive and letting it play master, or, alternately and if it's within your budget, getting a third, bigger, newer hard drive and installing windows onto it. kinda a fresh start and allows for further expansion.

[edit: i guess i didnt really answer your driver question. I don't think just copying them would work without many issues, but i don't have a better idea, either.]