Instead of using a TCL script, you could just make your PSF in charmm, and convert it to a NAMD format PSF using a utility on the NAMD website, I think it's called charmm2namd. You can do the same thing with a coordinate file (crd2pdb).

I'd recommend doing all your model building and analysis in CHARMM, it's much much easier than anything with tcl scripts.. part of the reason the 600$ is well worth it.