I've dug an old road bike out of the garage for the winter and need to upgrade the drive-train, I'm happy about most of what I need but but I'm not sure about the rear hub (an old Shimano Ultegra)..
..Will I need to change the rear hub/wheel to accommodate a 10-Speed cassette?
Answer: No you don't need a new hub.
However, you will probably need to put a small (~1mm) spacer at the back of the cassette, otherwise you won't be able to tighten the whole cassette down. Also be aware that prolonged use of a 10-speed cassette on an 8/9-speed freehub body will cause dents to form in the freehub body (because the 10-speed cogs are so narrow). The 10-speed freehub bodies have taller splines, so they avoid this problem (but don't work with 8- or 9-speed cassettes).
Assuming the hub is a freehub design (the freewheel mechanism is in a splined body onto which the cassette (sprockets) fit), no. 8, 9 and 10 speed cassettes are all the same width.
