I'm not an expert, so this might be nonsense, but I think it's something like this.
Bass signals need a bit of boost, usually either from an on board preamp, or from a preamp contained within a pedal or an amp head. Plugging the bass directly into the microphone socket won't do anything, and if you're using an active bass or going through an outboard preamp, this may be overkill. A jack-to-USB is probably not viable.
What you need is some kind of unit like this
http://tiny.cc/wwegk and some kind of corresponding software, like ProTools or something.
Plugging a bass directly into a laptop will do either nothing, or possibly (blind speculation) damage something.
This might not be true ^^ as I say I'm no expert, but that's how I think it works.