If you format the iPod for PC, it can be read by a Mac BUT NOT THE OTHER WAY ROUND.
As far as syncing is concerned, you cannot sync the music libraries on one iPod with two computers, as every time you sync with computer 'A' it will wipe of the music from Computer 'B' and visa versa. You can, however, manually manage the contents on the iPod and "click and drag" songs from both computers.
I am assuming that you can manually manage the contents on the iPod touch - something I am not currently able to do on my iPhone (although it is rumoured that this functionality will be introduced in a future firmware update).
Greg