Bicycle Mechanics - How Many Gears on my wheel?

I have Mavic/Shimano Open Pro Wheels and wish to upgrade from 9 to a 10 speed cassette. I believe my wheels were said to be 8/9 speed compatable when I bought them. (I am not sure that 10 speeds were out at that point.) Is there any reason why this wheel would not take a 10 speed cassette?

Thank you.

If it has a standard Shimano 9-speed freehub (e.g. FH-5500,6500,7700, etc.) it should work fine. It will, however, require a 1mm spacer as the 10-speed cassette has slightly less width.

see:
http://bike.shimano.com/publish/content/cycle/sac/us/en/technical_service/compatibility_charts/road_compatibility.-MainContent-0003-DownloadFile.tmp/9_10sp%20cs_fh_wh%20compatibility.pdf.pdf

It should accept a 10-speed Shimano cassette and, IIRC, the 1mm spacer accompanies the cassette.

Thank you for your responses. This is good to know. I have another wheel question, I might wish to get a new hub, are there any compatablilty issues with my wheel and any road bike hubs? Is it a big job to replace the hub or does it require specialized tools and skills?

Thanks again.

Replacing the hub is a project. If you look at your wheel it's obvious that you have to unlace all of the spokes in order to replace the hub. Relaceing the wheel isn't all that hard but it does require a degree of patience and skill.