Building a new system with both XP and Win7

[hunter301]

I am looking to build a new system with dual hard drives were I can run both XP based games and Win7 games.
I built my old system back in 2008 but it is still an ATX case. Lian Lee P65. Has slides were everything can be upgraded by sliding out the idividual parts without having to dig into the system to much.

I guess the first question would be can I still use this case todays motherboards, graphics cards, etc...? Case was over $200. and I would like to reuse as much from the old system as possible. Case, CD/DVD drive, Sound card. (I had a very high end sound card at the time. Was made to be used for all types of sound editing, recording, etc..)
I realize I'm going to have to upgrade my graphics, most likely the motherboard with CPU's. I don't want to end up buying a graphics or motherboard with quad CPU's that won't run say windows XP or some of the older games. Will the newer motherboards and graphics cards run XP?
Nothing more frustrating that spending a bunch of money on a new machine only to find out it doesn't run a game for something stupid like the game company didn't figure their game for a certain graphics card.