? set focus to a textbox when userform opens

I'm creating a userform for editing membership records of a small organisation. So I want the focus to default to textbox tboxFind which is used for searching the data.

I've put tboxFind first in the tab order, and in subroutine Userform_Initialize, the last line is tboxFind.SetFocus

Using Excel2000 on Windows Vista, it works OK.

Opening the same workbook in Excel2000 on WinXP, no textbox has the focus when the form opens, but once the user has started to use the form, the focus defaults back to tboxFind, as it should.

So why is the focus not where it should be when the form opens in WinXP?