Ok, these things are not cheap, you need to get Legal copies of serious tools if you plan on actually learning them.
fucklob: You have no hope in hell of licensing Gearbox's Code. Unless you have a spare design team, a publishing company, and a great royalty deal for gearbox, forget it.
Anything to do with releasing a standalone mod: Forget that too.
As for the models, if the game is Based on HL1 engine, then there are probably converters out there. If there are none, then the people who made the game did not want you copying their models into your own projects.
...who have this program should put it up for download.
Please don't openly promote warez.