new build xfx mb with 4G of DDR2 have 2 XFX8600 vid cards with DDR3

I have a new build still under constution. MB is a XFX nforce 680iLT SLI with 4 gigs of Corsair DDR2 XMS2 matched sets. The vidio cards are 2 XFX GeForce 8600 GT XXX 256 DDR3 SLI. the question is will the DDR2 and DDR3 case a conflict in the computer I don’t see why they being 2 seperate things but I’ve been wrong before and will be again any in site in to this would be helpfull