can't mount external drive after erase

I have a 40gb hard drive that I erased and formatted as fat. Specifically, formatted as FAT, 0 data after trying 7pass and getting an error. I want to install the disk on my PC and reinstall XP on it. My problem is that when I did this I got an error (cannot remember type) and now the drive doesn't show up in disk utility, my desktop or my PC anywhere. I don't know where to go from here. I've tried a couple of Partition Managers, both on the Mac and PC with no luck. Also tried Diskpart from the PC terminal with no luck. I'm not very well versed at using terminal on either machine but it looks like I'll have to resort to it to solve my problem. I have an IBook running OSX10.58. My PC is a Dell 2400, Win XP sp3. Help of any kind appreciated.

Al