Using Windows Explore Command

[J]

My database organizes file names and attaches a document
link to them.

I have a table with the document information, and a "file
extension" category

I also have a form, through which the user enters data
about the file and the file extension. I am trying to
create a "browse" button (very simmilar to "attach"
buttons that are used to attach files to e-mails) that
opens the windows explore command and lets the user browse
for a file extension. When the user has found the file
(and thus the file extension) on the computer, he
clicks "okay" (or something of the sort) and the file
extension is pasted in the data field.

Anyone know how to do this, or have any ideas?
Thanks