Use vlookup to auto populate a combo box in user forms

Hi, I am wondering if you can help. I have created a user form and populated combo boxes with lists. In the form is customer details. I would like to user to be able to select either the name or the customer account number. If the select the Acc No the company name should automatically appear, likewise, if they select the name to Acc No should automatically appear.

I have no idea where to start with this as any examples I have found aren't working. The details for the lookup is on a sheet called "Customers" and the range will be 2:300 either column A or B depending on which field.

Thanks

Katie