Plug your bass in via a 1/4' -> 1/8" adaptor in GB create a new track, make is a 'real instrument' track, then set the monitoring for channel 1 mono, press 'r' to start recording and you're set.
GB has software amplification, no need for a mixer, preamp, or DI
It also has built in effects which are pretty damn good quality.
www.iCompositions.com is the biggest GB resource on the web right now, complete with forums and an auditorium to share your work, 50MB free webspace for your music for signing up.
