Yup, that's "General MIDI", and for most people it's actually built-in for Windows and not Cakewalk. Unless you put a virtual instrument into your MIDI track, it'll default to "Microsoft Wavetable Synth" which is just horrible sounding.
I recommend using a computer rather than a drum machine. Any old sequencer will do if you want to put a wee bit of work into it, and some will do it more painlessly than others. If you already own the computer, it's going to be around the same price as buying a poor little old drum machine, but will sound way better. You can do things like load REAL loops of an actual drummer:
Like THIS
Nothing beats a real drummer. $30 for this one disc, or $50 for your choice of 3... that's real drum loops played by a real drummer on real kits. Granted it's not quite as flexible as programming your own, but some people (myself included) are better off letting a real drummer do that kind of work anyhow. And the flexibility is still huge. I have one of their discs (Drum Werks V) and I could make several albums worth of songs without sounding repetitive.
Then if you want to program your own beats, you can always do it with about a bazillion different free plug-ins out there, or pay for something like Linplug RMIV.
Not to sound like a shill or anything (I realize I DO sometimes, but I'm just an enthusiastic user), but when Tracktion 2 comes out next month, it'll include the RMIV (mentioned above) and 4 gigs of drum sounds, both 'real/live' and electronic. It'll also include Amplitube for your guitar and bass amp needs, and a slough of other stuff. Plus, well, Tracktion.
Still, back to my original point-- any free or cheap sequencer will still do the job for you and do it better than the Boss unit.
Greg