As far as the hardware goes, there are no differences between the 3G PC iPods and the 3G Mac iPods. The only diffrerence is the software used to download and manage your digital music library, and the file system in which the hard drive is formatted.
The 3G iPod package contains software for both Mac and PC on a CD-Rom install disk; iTunes 4 for OS X, iTunes 2 for OS 9 for the Mac and Musicmatch Jukebox for the PC. All 3G iPod packages include an iPod formatted with the HFS+ file system for use on Macs as default. If you want to use iPod on a PC, install the appropriate PC software included on the install disk. The software will format your iPod’s hard drive with the FAT32 file system for use on Windows.
All 3G iPod packages include the proprietary dock connector to FireWire cable. There is a 4 pin to 6 pin adapter included for use with PC iPods. Also note that older 1G and 2G iPod models were separated into two different packages; Mac and PC.