Help using Mega to create data file!

[Robert Wolfgang Rumpf]

I'm doing more Homoplasy testing, and need to use Mega to take a 
Phylip file of a protein coding gene and reduce it to just the third 
codon positions, and then export this new file back to Phylip.  I 
can't figure out how to do this in Mega!  Is there an easy way, or do 
I have to manually delete the first and second codon positions? 
Thanks...
____________________________
Dr. Robert Wolfgang Rumpf
Dept of Oral Biology
The Ohio State University
305 W. 12th Ave.
Columbus, OH  43210
___________________________