Well, I will have to make a point that XP64 is bad choice to run premiere pro CS4. For a very good reason that the drivers for video card and your HDD system are not very well supported, which creates the problem for video card to redraw the screen, that is why you see the sluggishness on your screen when you move the time line and it takes to long to move the cursor to different point in the timeline. Windows Vista 64bit or 32bit does not have this problem because it has better drivers support, and premiere pro CS4 utilizing an 64bit optimization works much faster and better.
CS2 however does not have 64bit optimization and it is using a 32bit compatibility in windows XP so bacause of the extra window resorses it has better performance.
Perhaps you can update a driver for video card and maybe upgrade to Vista 64bit or min 32bit.
A hardware upgrade took care of this problem for us. Looked like a great wedding and editing.