I am a new user & this is probably easy, but I have several vendors and each one has a unique vendor number. I want to be able to type a vendor name in my form and have the vendor number automatically entered in the field. Of coarse, new vendors don't yet have a number. Vendor numbers are provided by a different department.

I would suggest using a combo box for this. Base your combo box on your Vendor table with VendorID being the first field, VendorName the second. Bind the combo box to the VendorID in your form. Now you can start to type in the vendors name in the combo box and the combo box will automatically start to fill in the name for you. When you find the vendor and hit enter the VendorID will be saved in the table your form is based on.