Using standard PS2 mouse with scroll wheel, plug in type min din.
Tried new mouse and still the same.
Scroll lines set to one.
Happens not only on MUDCAT but any place that requires scrolling.
Changed to USB mouse with scroll wheel....problem cured.

BTW, I thought I'd give AVG AniVirus a go and after I loaded it, IE7 also loaded itself, uninvited, just like that.
I felt I may as well get used to it as Cluin says. So far the only problems are finding my way around it's new format. I must say, as I get used to using it I'm finding it OK. No other problems so far and I can't be sure it caused the mouse problem.
Thanks for your help, T........