HI mmvica,
I'm an avid EQ2 player, and I would highly recommend returning the game and going for Guild Wars, which is similar but doesn't require a very beefy system. Guild Wars will play on your system as-is. So your son can make a warrior, wizard or necro.. play online with friends.. and you wont have to break the bank for hardware upgrades. It has no monthly fee either.
EQ2, while a great game, is one of the absolute most taxing games on the shelves.. bar none. 512mb of memory, even on the games lowest settings, will be a stutter and pause fest.. 256mb isn't even playable at all. To get anything that resembles possible gameplay, you'll want 768MB to 1 gig of memory right off the bat.
Add to this the game uses DirectX 9.0 and has heavy, heavy overdraw. This means even mid-range, $150 3d cards are barely adequate- again at the games lowest settings.
The cheapest videocard I would recommend for that game (note- cheapest, not yielding the best performance in EQ2) would be the 9250 256mb - $48
http://www.newegg.com/Product/Product.asp?Item=N82E16814102392
I'm assuming your system has an AGP slot. You'll also need to add AT LEAST another 512mb of ram (bringing you to 768MB) of you plan to play EQ2.
If your son is into RPG's, GuildWars or Everquest (the first) is a much better choice with a limited system. EQ2 requires a very, very modern and beefy system.. and even my highest end $1500 system is brought to it's knees by this game.