Guys, blame Adobe. And Microsoft! I have had every problem ever listed on one of these forums since going to Vista64 and Premiere CS4. And my system is a dual Xeon HP XW8200 with 16gb RAM and Matrox AXIO HD installed, connected to a SAN via fibre. And the system was integrated by a Matrox/ Adobe certified reseller to their specs. In other words, a professional broadcast suite.
Nonetheless, you just can’t win. My best advice is enable PAE mode to map as much hardware above 4gb as you can, assign Premiere realtime RAM priority, and keep your projects as small as possible.
And then pray. Or move to Avid 😉