I think but can't be sure but this sounds like a memory/device mapping problem that we see with old gear. You might get around that by dropping RAM back to 1 or 2 GB and running a 32 BIT OS but why do that when a card from 2005 and on will likely cure this.
I am running Win7 ultimate...I had a raedon 9600 ati video card that died with a Rad tv tuner 650 pci. I replaced the 9600 with an nvidia 128 meg vid card. now Win 7 media center will not recognize the tv tuner any ideas? Email me direct @firstname.lastname@example.org