|It's not worth as much as you think.|
An assembled unit is always worth less than the sum of the parts. And add to that - you're "Joe Nobody" - you're not a recognized computer builder such as Dell, Gateway, HP, etc. The buyer has no idea of your computer expertise & you probably won't be offering any type of warranty or tech support, right? Would you be including legal copies of Vista (DVD + COA) & any other software that you have installed?