Dear LJ: Help me not want to throw my computer out the window?

[kitchen_kink]

motive_nuance offered to help me out with this, but he's been absolutely swamped lately and so I would feel bad to ask him right now. Besides, I might be able to do it myself, with a bit of help. :)

My computer is a Mac iBook, about 5 years old. It runs Mac OSX version 10.4.11, and has a 1.2 GHz Power PC G4 processor. It has 256 MB of memory, which I think is where I'm running into problems.

I've never considered myself a "power user," but at the moment, using, say, a browser, the Mail program, and Word at the same time causes the machine to slow down considerably. iPhoto and iTunes slow it to a crawl unless they are the only things running.

I'd like to add more memory to the machine - I think that would solve a lot of problems - but I'm told that going to the Apple store and having the Geniuses do it is going to cost me a lot more than I really have to pay.

So: how do I do it? Where do I shop, how much do I get, how much should I expect to pay, and how the heck do I install it?

Thanks, LJ!