I have a Core i7 with 8GB of Dual Channel memory and a Radeon 4850 graphics card.

With Windows Vista Ultimate 64bit I'm having numerous problems. I've had the machine 6 months and I'm still experiencing graphics driver issues (card has been swapped out) to the point where I will need to return the unit.

Hence, the recommendation to use a 64 bit operating system, while providing access to more memory, may cause problems in itself and needs careful investigation.