Flash Video is playing smoothly on my Windows 7 64bit system! Unfortunately, the fix will only work if you have a second hard drive installed.
The stuttering is caused by how Flash and Windows is handling the Flash Video stream in memory. The system is swapping between the page file and the system memory causing hard page faults.
Requirements: 2 Hard Drives installed
Solution: Create a second pagefile on the second disk equal to amount of ram installed in the system and reduce the pagefile size on the primary disk to 300MB.
The url below has decent instructions with nice pretty pictures on how to make the changes.
Hope this helps some folks. I've been running 720p without any issues since I made that change.
Intel Core 2 Quad 9550
Gigabte GA-EP45-UD3P MB
4gig DDR2 RAM