VBA UDF to populate textbox in UserForm

Hi -

This seems like it should be easy to do, but for the life of me I can't figure it out. What I'm trying to do:

When a user opens up the file, a User Form will display using the Worksheet_Open event. (this is working fine).
I've got a Textbox on the UF that I would like to populate with the value from the following function.

Function UDomain() as string
UDomain - Environ("USRDNSDOMAIN")
End Function

I can complete this by first sending the result to a cell in the worksheet and then bringing the value over to the textbox, but I'm looking for a way to bypass putting the info on the worksheet.

anybody know if this is possible?

thx.