I'm trying to help but I don't really understand your question.

Is DR3456 the name of the picture you want to open or the Part Number?
Are they different or are they the same?

I don't understand this part: "I am locating the parts and associated
part numbers from a drop down list in Excel." Does this mean that you
have a list of part numbers in a range and the combobox, or whatever,
is showing those numbers?
If thats the case then you can use the value of the selected item,
which I'm assuming is the part number, in the drop-down list in a
VLookupFunction, and return the picture name. Then can open up the
picture.

Here a sub that will insert pictures onto your worksheet.
The name of the pictures are found in Cells "A1:A6"

Public Sub InsertPicture()
Dim pictureName As String
Dim fileName As String
Dim cell As Range
For Each cell In Worksheets("Sheet1").Range("A1:A6")
pictureName = cell.Value
fileName = "C:\Program Files\Pictures\" & cell.Value & ".jpg"
Worksheets("Sheet1").Pictures.Insert(fileName).Sel ect
Next cell
End Sub

If I didn't help you too well, explain in more detail what you mean.