Lookup value from different list

Hi,

I presume we're talking about a list of users who don't exist in AD? If the users exist in AD then you can find that information directly from AD rather than maintaining a separate list.

If it's the case that these users do not exist in AD, then you can add a control for your user to enter the ID, and then using the List Lookup control, look up the list with your users in, and there is an option for filtering in that control that will allow you to select the column in your "user list" that contains that ID, and filter using the named control where your user will enter their ID.