David,

Thank you for your time.

I'm sorry I didn't describe my problem more clearly, let me try to do that now. It is the Thumb (now I know what it's called) that I am having problems with. While I'm moving the Thumb the List appears to be frozen, only reflecting the change in the Thumb's position when I release the mouse button, in other words when I let go of the Thumb.
For example: suppose the list contains names, sorted alphabeticaly. If you want to look someone up whose name starts with a 'j' but the visible part of the List points to names that start with an 'a', you can do that quickly by jumping into the 'j' neighbourhood by using the Thumb, so long that you get an immediate visual feedback of how far down you reached in the List. Well this is what isn't happening. Without this feature, using the Thumb is like searching blind, not knowing which part of the List will be displayed when you are done. I do get the proper visual feedback by scrolling through the List with the arrows, but it is a large list I am dealing with and searching this way is a very slow process.
Well, I hope this time I was a bit clearer and I would really appreciate if you could throw in any suggestions.

Thanks
Andrew