BAH! Well I'm beat - I put the GTS 250 into my sons pc, a dual core Athlon 5000+ with 4GB Ram and 7 Ultimate 32bit - this machine is pre-sp1 and pre-IE9 (two changes I made to my PC just before all the problems started) and it is having the same problems - using the GPU Tracker, fails to start the Core, and the standalone GPU3 software just keeps running test proteins.
*bangs head on desk*