LOL, we aim to please
The programs you need really depend on what you want to do. If you want to edit inis, use notepad or some of the other programs that have sprouted up for ini editing. If you want to see what's in generals, get Finalbig, a big viewer that'll extract the files that are in generals. If you want to edit music, that's relatively easy unless you're doing any kind of mixing, then you'll need SoundForge or CoolEdit. If you intend to model and skin, pick up 3DS Max or Gmax and the RenX package (was on one of the renegade sites, do a search for it on google) for the modelling end and then get photoshop or some other photo editing software (and maybe Chili skinner if you're serious) to make the tga's for skins and cameos. Pretty much it in a nutshell, dude.

Anyone else wanna add to that list, feel free.
Oh yeah, you'll probably want to get a CSF editor or else anything you make will have the MISSING tag on it, kinda annoying but that's usually something people fix last when everything else works.