I have the following cars:
'86 Trans Am
'94 Trans Am
'95 Corvette
'05 Tahoe

I want to be able to hook my laptop computer to these cars to help diagnose any problems and possibly "tune" the engines. What software setups to you recommend for OBDI and OBDII applications.

 

Look at the site below and see what is available for your cars (all are not supported for flash tuning).
The truck is not supported at all. For the truck, you will have to buy a TECH II I believe and that is about $6000.00.
With the Tunercat program(s), you will have to buy the proper DEFINITION files for each car.
The $EE Definition file should allow you to Flash the '94 Trans Am and the '95 Vette PCMs.
The other, '86 Trans Am, a chip will have to be burned, but the #32 Definition file will allow you to read the chip.

Tunercat: Tuner or RT Tuner and OBDII Tuner
http://www.tunercat.com/tnr_desc/do_tc.html

You will have to have at least 2 cables, one each for OBDI and OBDII. Then there are chips that have to be erased and burned for the NON-FLASH chips with your new tune.
I think the '94 Trans Am and the '95 Vette can be flash programmed with with the Tuner program and the OBDII cable.

Its all confusing at first, but look at the site and it will become easier to understand.

Look at the TTS Power Systems for the cables and Datalogging software. The datalogging software gives you 20 free uses before you have to pay for it.

http://www.ttspowersystems.com/

You may want to look at this site also. He has chip erasers and burners I believe.

http://moates.net/

Take all this with a grain of salt, but this is the jist of it. Others will come in and correct me if I'm wrong.