How do I change hammer so I can map for HL2 Deathmatch? I've installed it, but it's not in the list of games to map for.

1. Right click on Source SDK in the Tools tab of Steam
2. Select "Properties"
3. Click the "Set Launch Options"
4. Type this: -engine ep1
5. Click "Ok"
6. Click "Close"
   Now when you open the SDK, it should show HL2DM as a option. To be able to map for Portal and the OB games again, just delete the "-engine ep1" you entered.

Else, launch your Steam client with the option -beta srcsdk0122 after the path to the executable. (ie: C:\Games\Steam\Steam.exe -beta srcsdk0122)
Then, a beta SDK will be downloaded and you will now be able to switch between engines when launching the SDK (along with a bunch of new features). By the way, the beta is stable.

sweet, thanks alot