Formatting ipod for mac & PC?
If you restore it on a PC and format it for Windows you should be able to use it on both platforms. Strictly speaking using a Windows formatted iPod on a Mac isn't supported, Apple currently only supports using the iPod shuffle in FAT32 format on Mac. What this means effectively is that if you need to apply a firmware update for your iPod and you wanted to maintain the Windows format you would have to do it on a PC.
Alternatively there are third party programs that will allow you to use a Mac formatted iPod on Windows, this is one for instance gets good reviews: XPlay 2
You can read another user's experience of using XPlay at this link: iPod on Mac and Windows