Upgrading RAM

[Jaskohouston]

I have a standard Dell (I believe the 2400 - I'm not at home right now, and my Dell account won't let me access my purchase invoice to find the exact model number) that I purchased in August of 2004. It has 256 MB of RAM. Now that I have been using PokerTracker, and PokerAce, as well as having ITunes on my computer, I feel like the amount of memory I have is what is causing the relatively slow performance. It's not terrible performance, the computer just lags every so often, as well as getting the "virtual memory too low" warning. I know it's not spyware as I keep up with checking/eliminating that using a few spyware trackers.

Here's my questions:

1) Will 256MB more be enough? can I get 512MB extra if all I currently have is 256? I remember reading that both cards have to be the same size?

2) Can I just buy any card? I'm assuming because I have a pretty normal computer that what I would buy to install would probably fit in that computer?

3) Can I install this on my own fairly easily? I'm not exactly technically savvy, I've never installed anything on a computer, opened up the case, anything of the sort. Should I get it done professionally to avoid any disasters?

Any other comments upgrading memory would be welcome. I like the computer, I'm going to get a 2001FP to go along with it, I would just prefer it handle running multiple applications a little smoother.