As of yet 2GB Ram provides little to no advantage in games on XP. Gamespot did a benchmark and there was less than a 1% advantage on Oblivion, NWN2 etc.
That's why I refrained from upgrading to 2GB till I got my new comp. By then I thought what the hell, might as well.
Where 2GB would help is in future games and maybe if you go to Vista, but DDR2 667 is a good speed and so you did well for that price.
Here check out these Vista benchmarks, except just look at the 1GB and 2GB comparisons for the games on XP:
http://www.gamespot.com/features/6164940/p-3.htmlWorld of Warcraft: The Burning Crusade, 1600x1200, 2GB memory = 111 FPS
World of Warcraft: The Burning Crusade, 1600x1200, 1GB memory = 113 FPS
Oblivion, 1024x768, 2GB memory Windows XP = 62 FPS
Oblivion, 1024x768, 1GB memory Windows XP = 61 FPS
Company of Heroes, 1024x768, 2GB memory Windows XP = 182 FPS
Company of Heroes, 1024x768, 2GB memory Windows XP = 181 FPS
Neverwinter Nights 2, 1024x768, 2GB memory Windows XP = 47 FPS
Neverwinter Nights 2, 1024x768, 1GB memory Windows XP = 47 FPS
There you go. So yea it is a myth. 1 GB memory is more than sufficient for any gamer on XP, yet so many of us have wasted money on the extra mem. We are dumb.