Need Help To Use MY Hard Drive

Hello,
Hi guys, My problem is kinda complicated. I have a WD 500gig external hard drive. I primarily used it on my pc laptop for more storage room, my laptop was a pc that used windows vista. Now i'm trying to use it on my desktop computer which has windows xp professiona and am using service pack 2 l. Now it shows up in the windows explorer as local drive(g:) and not as a my book icon, and when i try to open it it says i have to format it which of course i don't want to do. Now I've tried a few of your guys suggestions such as trying to find that firewire 1384 but i can't find it in network connections, i've also tried relabeling it and it doesn't give me that option in disk management and if i try it in windows explorer it just says that i have to format the drive to relabel it.
So if any of you have any tips, words of advice, come across this problem and fixed it or anything please let me know