Getting 1Gb DDR, Worth it?

Recently my motherboard (Asus A7S8X-MX) died and I had to buy one by Axper (I think its a budget Gigabyte thing, has the same stuff in BIOS, including the Ctrl + F1 thing) And the Axper has 3 DDR slots, at the moment I have 2 DDR400 512Mb Sticks in Two of the slots, would it be worth it for me to buy a 1Gb stick to have 2Gbs? (I won't be able to upgrade for a while now that the motherboard died, as well as my PSU >.< )

Specs: AMD Athlon XP 2600+, 1Gb DDR400 Ram, nVidai GeForce 6800GS 512Mb AGP.

I usually have iTunes, Firefox, mIRC, Windows Live Messenger, Sygate Personal Firewall and AVG anti Virus running when I'm not playing Games, and the games I play are NfS Carbon, Most Wanted, Sims 2 with all Exps, GTA San Andreas with the SAMP mod, Oblivion, Battlefeild 2 and Star Wars: Empire at War.

Well, on the Axper site they use gigabyte.tw email addresses, and the cheapest 1Gb Stick I can see is for $61 dollars, so I'll look into buying that then, Thanks!