So, me and my amazingly awesome guitar friend just went by and picked up a Tascam Ministudio Porta 02 MKIITascam Ministudio Porta 02 MKII at my grandparents house. (My grandfather had one he said he would let me use.) We picked it up and took it back to my house. We sat and studied how exactly we where going to use it and what we where going to use to record it. We decided that we would take our speaker cables, and have one going from the head to the cabinet and the other speaker cable to the head into the "Mic One" and "Mic Two" sections on the recorder. My amp is a Stereo Head and Cab and my friends is a mono. So we started jamming into it to record, and when we played it back, his sounded clean (he was playing the rhythm of the intro to Sweet Child) and mine sounded like a horrible techno distortion.

We had 2 stereo speakers running from the recorder so we could play back when we were finished.

Anyways, why does it sound like ****?
Was yours coming out of one speaker while his was out of the other? In that case check the speakers and see if they're both working properly on a song that you know is recorded properly.

If you used actual microphones (although from your description it seems as though you just wired it right in):
If you have a stereo head, try micing the outside of one of the cones (not in between the two) and see what happens. You could possibly be getting some phase problems between the two speakers, although I would think it unlikely.

Try recording his section from the other mic and see what happens (just point the other mic to his amp, don't change the inputs or anything, physically move the microphone).

If you didn't use mics, switch the cord from your amp to his and vice versa, keeping them in the same line in jacks on the Tascam to see whether it's the cord or the input itself.

If none of those work, write back.
Stupid idea, there's a reason it says ''mic'', it can't handle the power of the head and it's being overdriven. You need to mic them up like it says or plug your guitar directly into the device rather than your amp.
dont run a speaker out of an amp to your mic input of any recorder, youl'l burn out your amp and recorder.......

I suggest getting a cheap interface and running it with a PC. Interfaces are low in price these days and are much better than those small tape recorders.

Products like the m-audio Fast Track USB allow XLR input and have a preamp on board, it also will give you unlimited tracks.
For software run Audacity or even Reaper.

BTW, recording questions and products like this should be in the R&R form