What kind of program would I need to download to do that?
For meshes: Blender, Maya, 3DS Max, etc.
Blender is the only free one, but you can get the other two free as well if you are a student somewhere.
For texturing: Photoshop, Gimp, Mudbox, etc.
Gimp is the only one that's free, but again, I believe you can get the rest by having a student email. Maybe not Photoshop.
You only need one of each. I've been using Maya and I'm liking it so far. They're all going to have fairly steep learning curves if you've never done anything like this before. I can't comment on texturing since I've never actually tried doing it yet.