Mousekeys - cannot get this to work correctly

As I suffer from bad RSI I thought I'd try using the mousekeys function. This apparently enables the numeric keyboard to be used instead of the mouse. However, all that happens for me once this is enabled is that pressing 5 acts as the right click button - and that's it! I'm using xp. Anyone have any ideas as to what I can do to get this facility working as it should?

Thanks in advance! :)

Here's an article if it's any help:

http://www.microsoft.com/enable/trai...mousekeys.aspx