Need help with an old Apple Mac G5 Desktop?

Hey guys so my friend got this Apple Mac G5 from someone and he wants me to fix it up so he can sell it...

The Operating System which has Mac OS X Jaguar on it seems to be messed up or something, sometimes it freezes but the biggest problem is the Internet browser, for some reason it doesn't load webpages correctly.

Anyways several questions answer any. It doesn't have to be all of them.

1. How would I go about finding out what Mac G5 computer this is? Apparently several different models were made between 2003-2006 before it was discontinued.

2. How easy would it to be able to get Jaguar OS X? I have a feeling I'm gonna have to do a fresh install on this thing and I'm just wondering how I would go about getting the OS.

3. Is it actually worth selling? I personally don't think so. He really thinks he can get $450 out of it.. but the thing is just so outdated! not to mention it can't handle the latest version of iTunes and what not meaning newer Apple stuff like iPods and iPads aren't even gonna work on it!

anyways any help would be appreciated... even if he can't sell it he would still like it fixed up to use.