Need Hard Drive Help, New to the site, so please Help me!!

Ok i have an old dell with a pentium 2 in it, no biggie, it had Windows 98 on it a while back and it crashed, so i stuck the dell's hard drive in my brothers computer and installed windows XP onto the Dells Hard Drive ( Which i believe is a fat32 System Drive, Mextor or something like that is the name ). The Hard Disk shows up as an extra disk drive on my brothers computer and works just fine, it shows all the windows components and folders, Installation was sucessfull. But when i stick the hard drive back into my dell and try to start it up it says " Please Remove Disk or Other Media ". I was wondering if any of you could help me with this!!! or any clues at all. I made sure that i had a Boot.Ini in the windows folder cause i read that on a thread on another site. I also have a floppy disk with a boot.ini file but it says I/O Error please replace disk when i try starting up off of that. PLEASE HELP ME GUYS.