Doing a little research around, I've found the following information about the programs:
MSDTC is the Microsoft Distributed Transactions Coordinator. Details on it are a little sketchy (I'm not a network tech) but it seems to relate to things such as SQL servers and database administration. Typically this sort of thing isn't used on home systems, but it may be required for certain programs, so it's best to keep it on (someone might be able to correct me on this).
DLLHOST primarily is used in IIS (Internet Information Server). Some firewall programs seem to use it too, as it allows DLLs to be run (similar to RUNDLL.exe in the Win9x systems).
Note that the above could be wildly wrong (It's 10:30 at night, and I'm tired, not a good combo

) but my research leads me to these conclusions. If someone wants to correct me, go for it
