The problem with having popup forms is that the Form owning the popup will lose focus. However this can be corrected but it's not the most simpliest task to do so. All VB applications have an invisible Form with the classname ThunderMain. To fix the focus problem you need to subclass this window and stripping of the WS_VISIBLE style at the correct time. The correct time is when your main form is created.
This means it has to be done before Form_Load since by then the Form is already created it's just not shown yet. Anyway I wrote a ActiveX DLL that takes care of all of this for you. You can use this DLL project for any types of popups and floating toolbars and such. The only thing you have to do is to create an instance of this object in Form_Initilize and call the AttachParent method. You must also call the DetachMethod before your Form is destroyed (in Form_Unload for example). Note that this is done for your parent form, not the popup form itself.
The attach project group contains the DLL + a demo project showing a popup form with a ListView control. The demo app just have a regular CommandButton that shows the popup but you can easily change that so that it looks like a combo box instead (see the attached image).
Private pop As PopupMod.CPopupModifier
Private Sub Form_Initialize()
Set pop = New PopupMod.CPopupModifier
Private Sub Form_Unload(Cancel As Integer)
If Not pop Is Nothing Then
Set pop = Nothing