Explorer.exe doesn't exist

Hello,
ok so my antivirus must have deleted my explorer.exe file and i can't find it... anywhere is there any way to fix this problem without my bootdisk?
btw: i have vista home premium i tried copying the file out of my other computer, buttt i think that it won't work cause my desktop is xp and i'm having problems with my vista and i'm pretty sure that it won't work anyway