Shimano 8/9/10 speed cassettes are all the same width, and fit on the same width freehub body. 7-speed cassettes were narrower, and fit on a narrower freehub body, and if you wanted to run 8, 9 or 10 speeds on a hub with a 7-speed cassette you'd need to replace the 7-speed freehub body wtih an 8/9/10-speed freehub body, and redish the wheel.
But in your case, nothing needs to be altered.
Btw, Ultegra/Open Pro wheels are usually good ones. Ultegra hubs are as top-notch as a hub needs to be, and while Mavic Open Pro rims have problems every so often, they're still a very good rim that's the de facto standard among road rims, and they have that status for mostly good reasons. Just make sure the wheels you're getting are built with butted spokes.
Last edited by TallRider; 09-19-06 at 01:00 PM.