code to merge and/or append and/or save sections of WAV files?

can someone post code on how to

* merge 2 mono wav files into a single stereo wav file (one file in
the left channel one in the right)
* append one wav file to another
* merge 2 stereo wav files into a single stereo wav file (specifying
the "mix" for each channel - the volume for file #1 left and file #2
left, and right, respectively)
* save a section of a wav file (starting second, end second)

VB.NET code or a .NET assembly would be best for my purposes, but any
language would work, all it should be doing that is system-specific
would be binary reading / binary writing the data from the WAV file on
disk...

thanks