if he likes MOHAA get him Call of Duty he will fall in love all over again
then after COD which is way more graphically intense he'll tell everyone he needs a new videocard so you make him wait and buy him a videocard for his b-day. Hopefully its after April so that way the new cards right now like 9800Pro will drop significantly and they will be an awesome buy for cheap. Also the new generation will come out and if he adds $100 of his own he can get the newest and greatest
You should only buy a new videocard when you cant play the games you like any longer smoothly at say 1280x1024 or whatever he prefers (with AA/AF on/off?)
so iwth medal of honor i am sure its running just fine i have 3.06 with radeon 8500 no problems at 1600x1200 and his videocard is better than mine already so....
if he is getting 80FPS now yes a new card like 5900nu will give him double, triple whatever it is but no one can tell after 60 steady i bet.
So in conclusion until he has a game that runs slower than he lieks then there is no point of getting him a videocard now but if u really wanna give him that present 5900 NU for 199 XFX at
www.pricewatch.com you can search for them they are cheap