Concatenate cell values for duplicate numbers

I have an speadsheet that has two columns. Column "A" is a list of part numbers. Column "B" Reference values.
The Part Numbers can have muliple values listed in column B. I need to concatenate those values into a single cell with comma delimentation.
THIS IS EXAMPLE OF THE SPREADSHEET:
P/N H-D#
105200 96600-36B
105200 98705-85V
106400 96815-46
106400 98715-85V
109736 6762-B
109736 70011-81
109737 67697-81
109737 70097-75
109738 6762B
109738 70069-65
109739 67621-94
109739 70011-81
120010 38619-71B
120010 40037-79
120010 40037-79A
120011 38599-83A
120011 40007-36A
120011 40007-36B

OUTPUT NEEDS TO BE:
P/N H-D#
105200 96600-36B, 98705-85V
106400 96815-46, 98715-85V
109736 6762-B, 70011-81
109737 67697-81, 70097-75
109738 6762B, 70069-65
109739 67621-94, 70011-81
120010 38619-71B, 40037-79, 40037-79A
120011 38599-83A, 40007-36A, 40007-36B

Does anyone know of a way to do this?
Any help would be greatly appreciated.
Thanks
Joanie

I get an error

Sub test1()
Dim sTemp As String, r As Long, lastrow As Long
lastrow = Range("A" & Rows.Count).End(xlUp).Row
With CreateObject("Scripting.Dictionary")
For r = 2 To lastrow
sTemp = Range("A" & r)
If Not .Exists(sTemp) Then
.Item(sTemp) = Range("B" & r)
Else
.Item(sTemp) = .Item(sTemp) & ", " & Range("B" & r)
End If
Next r
For r = 2 To lastrow
sTemp = Range("A" & r)
Range("B" & r) = .Item(sTemp)
Next r
End With
Range("A1:B" & lastrow).RemoveDuplicates Columns:=Array(1, 2), Header:=xlYes
End Sub

Do you know what I am doing wrong?
I am really a novice at Excel.
Sorry.
Joanie

Neil,
That worked PERFECTLY!!!!! Thank you so much.
This just saved me.
Joanie