heres the mix I sometimes use if I'm desparate and working on really dirty matts:
25% Simple Green
15% Meguiar's EXTRA!
10% Tide Laundry Soap
50% HOT water
shake vigorously in spray bottle. Spray matts/carpets down liberally, agitate in with brush. Allow to sit 1-2 minutes, come back and re-agitate. Use one terry towel to remove most of initial residue. Follow up with a liberal spraying of JUST water (luke warm this time)...... agitate with CLEAN brush, then blot out with terry towel. Final step is spray down with a misting of cold water and use a 3rd towel to wipe up, do not brush this time. Allow it to sit for about 5 minutes and air dry, then follow with the vacuum (if you have a wet/dry shop vac it works great, otherwise wait about 15 minutes for air drying and use your regular vac)
you SHOULD have spotless (or near spotless) carpets now! :xyxthumbs