The line in wants a line level signal...your bass guitar doesn't put out a line level signal. Yes, a DI box / preamp of some sort is really required. You could look into something like a Bass POD or Sansamp Bass Driver DI box...or even an ART Tube MP would work.
If your bass has active electronics you should be able to plug right into the line in on the sound card. Active electronics will pretty much give you a line level signal, which your line in on your soundcard will accept. Of course plugging straght into your soundcard won't sound good, but you can jot ideas down that way until you get a preamp.
The line in wants a line level signal...your bass guitar doesn't put out a line level signal. Yes, a DI box / preamp of some sort is really required. You could look into something like a Bass POD or Sansamp Bass Driver DI box...or even an ART Tube MP would work.
Thanks to all who've responded.... does a bass amp combo w/ speaker function as a preamp as well? I think I recall seeing an output jack on some amps that I've looked at. If so, what features/controls (EQ, etc) should I look for in an amp to be able to optimize recording potential?