Win2k3 is worth looking at as an alternative (since you've already bought it). ;-) Check if other Win2k sites have upgraded yet. Many wait for a certain number of SPs before taking the plunge.
You are also using Windows 2000 Advanced Server, and that's no slouch. It's designed to run on fast, multi-processor boxes.
I'd sure rather see this problem nailed down before migrating to Windows 2003 Server... that could be just one more direction to point (middle) fingers.