Help! Reformatting an external harddrive with OS 10.4

Hey, I'm having a bit of a problem and was wondering if anyone here could help?

I have a Mac format external harddrive which I now want to use with my new windows laptop. I know that I need to reformat it to FAT32 in order to make it cross-platform compatible. Problem is, I don't seem able to do so. All online guides I can find suggest I use the erase function on Disk Utility on Mac OS X to reformat it as MS-DOS - however this option is not available in the drop down list where it apparently should be! (I'm using OS 10.4)

My windows machine will recognise that the device exists, but only in device manager, where I don't seem able to format it. Guides online say to do it in 'My Computer' but it doesn't show up there. (I'm using Vista.)

Any suggestions why I'm having these problems and how I can format it? At this stage I'll be happy to just get it to work with windows, but ideally want to make it cross-compatible for a while to move some stuff from my Mac harddrive.

Any help would be muchly appreciated.