Can I use my iphone 4 on any computer?

I have a PC. If I want to upload music to my iphone from my PC, can I? Or, do I have to have a mac?

Added (1). Can i just add the songs from my windows media player? Or do they have to be on itunes?

You can use it on any computer if you want to make full use i suggest getting iTunes if you haven't already.

Yes yes you can all you need to have is an application called as "iTunes" on your pc. Download the latest version of iTunes from apple site. It's a freeware and open software. Then you'll be able to connect your iPhone to pc.
And This will work for sure.