If I may offer advice, don't go out and buy a stack of expensive applications with the idea of becoming a Poser vendor. You'll never make enough money to repay your investment anyway; and what if you decide you don't want to do this after all? Faced with a daunting pile of learning curves, you may well turn tail and run. :) The added stress of needing to produce something won't help in that situation.

Make stuff for yourself first of all, because you need it. Start simple and work up. Once you have some things you're proud of, give them away as freestuff and see if everyone else agrees with you. ;)

The basic tools you'll need are:

• a modeller. These range from free to many thousands of dollars. All the good ones have demo versions - try them out and see which ones "click".
• a UV mapper, assuming you aren't 100% happy with whatever your modeller provides - and many people I know aren't. Again, there are free ones, but the high end of the price range isn't as high as it is with modellers.
• a painting program for texturing. You may already have Photoshop or something like that.
• There are a variety of small utilities which will make your life easier, but it's best to get those as the need arises, I think. In today's pay-and-download world, you can decide you need a CR2 editor at 12:00, and have one installed on your machine by 12:05. :)

Hope that helps...