Water Pump

I was hoping one of you could help me. My car recently began over-heating, especially quickly when it was moving slowly or not-at-all. Seeing as how speed managed to keep it cool, I vetoed the idea that the radiator was to blame (although I suppose that's the next thing to look out for), which left me staring down at the water pump. Pretty much, all I'm wondering is:

Based upon this generalized statement, does it sound like a mangled water pump? The belt is fine, and the weep hole is ok, although there's not much pressure is the system, it's completely topped up and I can occasionally hear a rough, scratchy noise from behind when the engine is shut off.

If so, does anyone know what's necessary to replace a water pump? Should I not try to do it at home?

If it is possible to do at home, could anyone help me out a little?

Hm... I don't know. I mean, the coolant lines do get hot, which they claim is a sign to look somewhere else, but I swore it was that bloody pump. Like I said, every now and then I hear a thump (not a backfire) come from where the waterpump is located approximately. Oh well, I have one on order, and even if it's something totally different and my pump is fine, I'll only be out $50. I just pray it's not the radiator. Although more and more, I'm starting to suspect it is (The radiator will start to steam up if the car overheats for a couple of minutes).