D10 Controller described a conflict event when departure traffic failed to maintain assigned altitude. The reporter listed TCAS as instrumental in preventing an even more serious situation.

Narrative

DFW was in a south flow configuration; as were the other satellite airports in the Metroplex. Aircraft X was departing IFR off of Runway 18 at Denton (DTO); initially on a heading of 190 degrees. After being RADAR identified; aircraft X was instructed to; 'Turn right heading 360; climb and maintain 4;000 FT.' The pilot correctly read back the 4;000 FT instruction. I had several other things going on across my airspace; which is why I listed the complexity as a factor. I watched the replay; aircraft X climbed extremely fast and he grossly deviated from his 4;000 FT restriction. While I was taking care of something else; I either heard the CA/CA or saw it blinking; but I could see that aircraft X was at 4;700 FT and at this point already slightly behind Air Carrier Y; an MD80 arrival at DFW. I told aircraft X that his altitude assignment was 4;000 FT and he promptly descended. The Arrival 3 Controller informed me that Air Carrier Y had responded to a TCAS RA and climbed accordingly. I informed the FLM and we watched the replay and I heard the DALR. Aircraft X clearly read back 4;000 FT; so I'm not sure what was going on in his flight deck that would have allowed this situation to develop.I was pretty busy with a range of operations and I had to climb aircraft X to 4;000 FT because there was another aircraft on the Runway 16L localizer at Alliance airport (AFW). In any event; the pilot was climbing rapidly through 4;700 FT when he instructed to return to 4;000 FT. It appears that Air Carrier Y's TCAS RA was instrumental in avoiding a collision.