If you buy music in the iTunes Music Store can those songs be downloaded at another computer or do the files have to be transfered by CD or file transfer methods? Does it matter if files are bought on a Mac and I want to listen to them from a PC?
Songs can be loaded onto three different computers only. If you sell a computer and buy a new one you can de-register it and register a new one.
I don't know about the Mac to Pc thing. I would think it would work, have you checked out Apple's knowledge base or the forums? They are usually a good source for info.
I believe it works, no reason not to. But the songs need to be transferred through CD or other physical means. Because Apple doesn't let you redownload the songs. Which is ridiculous, but I guess the cost of keeping the tunes on the server is too great (as in bandwidth)