Firstly - do take luc's advice, you need to normalise you database.
Once the database is normalised it then becomes easier to service the combo/auto complete fields because you would now have the concept of Master Tables or Static data.
I am assuming you are using winforms so this is how we do it.
Have a static class called MasterTables with a property for each table that services the combo's. In the getter have it check if a local datatable variable for the table is null and load it if required. This leaves the data in memory on the local machine. If the user adds a record to a master table you set the mastertables property to null and it will automatically be loaded next time it is called.
Caveat, this does NOT refresh master tables modified on other client machines, for that you need to wire up events back to SQL Server. I have never seen a need to do this with the type of apps I write.