Everyone is being sarcastic because it's like a joke.
1. you know how to make games yet you can't pick out a comp yourself
2. you didn't explain what you wanted
3. Supercomputer is a rather powerful thing....
Anyway, here is what i'd go for.
Intel i7 920 2.66 Ghz
3GB ram (Corsair 1gb modules) unless you want a 64 bit machine which I assume you o not.
Nvidia GTX 260 / 280, if the cost is too much for for the 9800GTX+ (this requires a taller case to fit the mobo) the card will take 2 slots.
Asus P6T SE motherboard (dual card support and supports i7)
HDD is really your choice, probably a 500GB
Here is the build:
http://www.ibuypower.com/Store/Configur ... px?mid=375