Hi wtubb,
If you want to combine TDMS files outside of DIAdem, you can just concatenate them with DOS commands in a batch file. The TDMS file format is made up of individual sections, think of an array of objects, where each object could contain metadata, channel values, or both. When streaming buffers to a TDMS file, the streaming program just adds more of these sections/objects to the end of the TDMS file. Each section contains a pointer at its beginning to the relative position (byte offset) of its end. So if you've got two TDMS files, TDMS1 and TDMS2, you can just DOS concatenate them together, and it's just like streaming the buffers/sections/objects of TDMS2 to the end of TDMS1.
If Mark's code doesn't suit you for some reason, I can provide example code of how to programmatically create and execute such a batch file in a DIAdem VBScript.
Brad Turpin
Principal Technical Support Engineer
NI