To get rid of vocals from a stereo track, sometimes you can invert the original wave and then add the two together. This can work because often the lead vocals are dead center in the mix, while other instruments are moved about a bit. Hmm, it might have been invert the left channel and add to the right, sorry not to recall specifics but there is a technique along those lines out there.
Hearing bassy instruments more than treble ones? EQ. Oh how I'd love it if one day music were distributed with a seperate track for at least the main instruments.
As for freeware/shareware, don't know. The trial of CoolEdit rocked (as did the purchased program) which became Adobe Audition. Perhaps even worth purchasing, but maybe a CoolEdit demo is out there you can find.