If the drive is smaller than 128GB, why not just format the whole thing as FAT32? If it's bigger, you might be able to just split it in half and partition each as FAT32. It's recognized by Macs and PCs. Otherwise, Macs have read access to NTFS. You could also format it as HFS, and get MediaFour's MacDrive. Gives PCs access to Mac filesystems.
If nothing else, try to partition it again, and leave the second part unformatted. Go into the Control Panel, Admin Tools, Computer Management, Storage, Disk Management. Format the first part with FAT32 (if it's less than 128GB), and take it over to the Mac. Make sure the Mac only touches the unformatted part, and format it as HFS. Then take it back over to the PC, make sure it has a drive letter, but don't let it format it if it asks you too. You may need to reboot, but you shouldn't have to.
This should be possible, I've seen it done.