Dropdown only showing certain options, possible?

On that drop down list, I assume that it is being chosen off a relationship from another table.

Look for the field on the table probably called [Related Purchase Order].  Then there will be a checkbox on that field  for 

Conditional values The values in this field depend on a selection in another field

Check that box and make the drop down choices conditional on the [Related Vendor] the POs field for [Related vendor] matching the [Related vendor] chosen on the first drop down.

Worked like a charm!  Thanks!

Let me ask this....Can I take it another level?  Here's the situation:  I use the process you outlined above and now see only the purchase orders for that vendor.  I have different purchase orders for different lines of service...we'll call them Directorate A, Directorate B and Directorate C.  Based on a field designating the Directorate the job is coming from, can I show only that Directorate's purchase orders?  Let me know if I need to clarify that a bit.

no problem",

So if you make a field which is a concatenated formula field called perhaps [Related Vendor - Line of Service] put it on the form

List("-", ToText(Related Vendor]),[Line of service])

 and then if your make a similar field on your purchase orders, then you can make the [Related Purchase Order] field conditional on those two fields matching.  Be sure to put the the first concatenated field on the form so that the form sees it.  Once it is working you may be able to hide it with a form rule.