Half complete hyperlink textboxes, Possible?

[Greyowlsl]

i have a form with a textbox, this textbox is linked to a table that has a hyperlink column. Now i dont know if this is possible but i want that when a user adds a new record using textboxes that the hyperlink textbox starts to add parts of the hyperlink (this is for a document database and the link is to the file on the main server). For example when someone selects 'Legal documents' from a combobox the hyperlink textbox places 'd:\Office\Legal'
then when they select another combobox it adds more till the link is complete and the user saves the new data into the database.

Thanks for your time