I have done this many times with cleaning interiors and it works wonderfully. Vaccum the area real well, get you a bucket of hot water (about a gallon) and take one scoop of oxyclean and dump it into the water. Let it sit for about 10-15 minutes, if you have a lowes/home depot/wal-mart in your city, pick up some Folex and Kids N Pets, spray some Folex on the "spot" and let it sit for about 15-25 minutes, after you have let it set in the carpet fibers, take a hard bristle nylon brush, you can get them at wal-mart or almost anywhere, you probable already have one, take the brush and dip it into the "oxy" water and start scrubing the whole area.
If you have a shop vac this would come in handy right now or even better a extractor. Extract the carpet and inspect the area. You will immediately notice how clean things really are. Whatever you use whether it be shopvac, extractor or with a good amount of towels. Try and make it dry as possible.
If your not satisfied with the results of the Folex, get out the Kids N Pets and work only on that spot from this point.