I went to tools/options and selected manual calculation.

Then I change the code to:

Private Sub cboPartnum_KeyDown(ByVal KeyCode As MSForms.ReturnInteger,
ByVal Shift As Integer)
Select Case KeyCode
Case 9 'Tab
Worksheets("QuotedPart").Range("d2").Activate
Case 13 'Enter
Worksheets("QuotedPart").Range("d2").Activate
Case Else
'do nothing
End Select
Application.Calculate
End Sub

This solves the problem of the "calculation loop" that I can't
determine the cause for.

However, it bring up these questions for me:

This file is an .xlt file placed on the network

1. If the use has other workbooks set to automatic calculation, how
will this effect my template? I'm going to use xlCalculationManual on
work_book open.

2. The user is forced to press F9--possibly several times--to complete
the quote. There are cells to populate with values depending on the
part number to include all the charges. I'm going to use
application.calculate on worksheet_selection change.

Dan