In systems with an IOMMU, we get DMA faults when the graphics card attempts to DMA to/from physical address zero.
Stray DMA considered harmful.
If its of any help I have a 64 bit system (based on Fedora 12) with exactly this problem using git versions of the kernel (2.6.34-rc2) and nouveau from freedesktop (obtained today).
While the system is idle I'm willing to try stuff out.
As mentioned in the redhat bugzilla this bug is fixed.