there are 2 issues with that custom built computer.
A. Better Parts vs Price
B. Overall Longevity
For about the same price of a 4400+ you can get an e4850 and have less heat with more performance. An 8800GT is fine and dandy but you can get an 9600GT or 9600GSO for a cheaper price.
Longevity, how long do you want the PC to last you. Adding the parts suggested would make it a more suitable environment for hardware because the processor is putting out 30-40 degrees less heat. Heat can shorten a PC's lifespan up to two years.
As for buying a PC, buying ibuypower PC off NewEgg would be cheaper thn the other.