Like TPAM said, all harddrives are the same until your format them 🙂
Macs can read FAT32, HFS+ and NTFS. They cannot write to NTFS, however.
Windows can read/write FAT32 and NTFS, but not HFS.
So if you intend to share this with a Windows PC, I recommend formatting as FAT32. If it'll ONLY be used with your Mac, I'd go with HFS+ (because...well, why not?)