as far as i know you should be fine. I have both a pc and a mac, if you format for pc you can use both pc and mac, but if you format for mac which is HFS, you WONT be able to use it with a pc which is FAT32. So your in the clear, lastly, the iphone has two partitions, on for system files(i.e. Jailbroke files, etc) and ipod files(music, videos, etc.) theres nothing you need to do to your phone since you synced and formatted for a pc, the only thing youll need to do is resync with itunes which will clear out your music. Hope i cleared everything up for you. But your a smart guy already, otherwise you wouldnt have bought a mac

ps. Im also in the bx, e233rd & whiteplains rd.