Thanks very much. Interesting how such a simple problem has such an evasive solution.
After going through about 3 pages of this thread it became apparent that fonts were a good place to look.
I am running Win 7 x64 and the Segoe fonts did not show at all, yet if I used Windows Explorer and went to c:\windows\fonts there was the whole set of them.
I simply double-clicked the first in each group (there are several variants, like bold, italic, etc.) and this brought up a font viewer with the option to Install, which I did. (If you by mistake try one that's already installed it will tell you and allow you to cancel)
Once I intalled the whole set (segoe*.*) everything now works in iTunes, including being able to type in the search box.
Thanks again
...tom