I think you should explore the Combo Props like Jason said.
But just for the record, to filter a UltraCombo its typically something like
// Set EpiUltraCombo Properties
this.comboTCRelatedOp.ValueMember = "ResourceID";
this.comboTCRelatedOp.DataSource = dsResourceAdapter;
this.comboTCRelatedOp.DisplayMember = "ResourceGrpDescription";
string[] fields = new string[] {"ResourceGrpDescription", "ResourceID"};
this.comboTCRelatedOp.SetColumnFilter(fields);
// Custom Values Filtering
UltraGridBand rootBand = this.comboTCRelatedOp.DisplayLayout.Bands[0];
//rootBand.Columns["ResourceID"].Hidden = true; // Make 2nd column invisible
rootBand.ColumnFilters.ClearAllFilters();
rootBand.ColumnFilters["ResourceGrpDescription"].FilterConditions.Add(FilterComparisionOperator.Contains, "Platen");
rootBand.ColumnFilters["ResourceGrpDescription"].FilterConditions.Add(FilterComparisionOperator.Contains, "Preco");
rootBand.ColumnFilters["ResourceGrpDescription"].LogicalOperator = FilterLogicalOperator.Or;
Some folks do it on BeforeDropDown