My friend is having trouble running Team Fortress 2 due to a "cannot read memory" error. Any ideas?

[Lordgeorge16]

So I was helping my friend install a new 2GB stick of RAM in his computer the other day (He was originally just at 478MB. Seriously). Took us a little while, and after my thumbs were nearly bleeding, we finally got it in. We started up his computer, let everything install properly, and he was good to go. So we tried out Team Fortress 2 after waiting for what felt like hours for it to finish downloading. We launched it, and after a few minutes in-game, it gave him the following error.
[quote=error message]The instruction at "0x164c03a2" referenced memory at "0x1794c42c". The memory could not be "read".[/quote]
We have no idea what it means, neither of us have ever seen this error before. Just to be safe, we tried out a couple of other games. Half-Life 2 ran just fine, and Portal 2 didn't close out on him like it used to (However, when we loaded a map, all the sounds were playing and the captions were on-screen, but everything else was entirely black for some reason, it's like someone popped Chell's eyes out of her head).

Any ideas on how to remedy the problem?

Also, I'm sorry if this is in the wrong section or if there's a thread for this, because I didn't see any.

My friend's computer info:
GPU: ATi Radeon Xpress 1100
2018MB total RAM (Approximately)
OS: Windows XP Home edition 32-bit
CPU: Intel Pentium 4 CPU 3.00GHz (2 CPUs)

[Quality Control]

[url=http://www.facepunch.com/forums/107]this[/url] might have been a better place to post this.