OK, fine. Try this:
*******
PartName = Part.GetTitle
If Right(PartName, 7) = ".sldprt" Then
PartName = Left(PartName, Len(PartName) - 7)
End If
PartName = "C:\" & PartName & ".igs"
*******
If you want the file stored somwhere other than the root of your C: drive, just replace C:\ with...