returning focus to Excel

I need to be able to return the focus to Excel in response to certain events in a userform.

Please look at this file if you don't know what I mean. I think it only works in Excel2000 because it contains a non-modal userform.

(broken link)

PS: I a similar question a while back and Ivan recommended they look at the application.inputbox documentation - I've been all over the help files and Microsoft site and haven't found anything.