Here is my advice. Seeing as I am A+ certified, and have been building computers for a while now, I feel there are a few important things to be noted.
First, do not skimp on the PSU. This is the most important part of your whole system, and you want it to be of good quality.
Secondly, metal cases generally stand up better to time and wear than do plastic cases. In my opinion, they also look better, but the case really only has to hold all your stuff, so material is a second thought.
Third, if you are only using the board to program your robot, you might look into getting a MoBo, CPU, VGA set. its lower end, but it will save you from having to buy a graphics card, and you might be able to find a small form factor, meaning a cheaper case as well.
Fourth, expansion cards are generally universal. As long as you are connected to the internet, you can generally just power off, plug in, power on, and it should work. You will probably have to go though initial set-up and whatnot, but thats to be expected.
I don't know what kind of budget you're looking at, but you could build a decent rig that programms PICs for under $600 if you tried.
If you want to take a look at how I'm setting up my own programming comp, PM me. I'd be more than happy to discuss specific components