Create a public class and give it a GetIcon method that returns one of the PictureBox's Picture properties.

Public Function GetIcon(ByVal Index As Integer) As _
    StdPicture
    Set GetIcon = frmIcons.picIcon(Index).Picture
End Function

If the main program is in its own project, load the DLL project, open the File menu, and select the Make Xxx.dll command to build the DLL. Then load the main project, open the Project menu, select References, and check the DLL's entry. If you cannot find the DLL, click the Browse button to select it.

After you have created the reference to the DLL, you can create an instance of the class and use it's public GetIcon method to retrieve the pictures stored in the DLL.

Private Sub optIcon_Click(Index As Integer)
Dim icon_holder As StorageIconHolder

    Set icon_holder = New StorageIconHolder
    Me.MouseIcon = icon_holder.GetIcon(Index)
    Me.MousePointer = vbCustom
    Picture1.Picture = icon_holder.GetIcon(Index)
End Sub