Grrr, Hammer seems as buggy as ever. First HL2DM will only load in the 2006 version of the SDK tools, which just renders empty blackness in the viewports on my ATI card. Then after setting it up manually to use the 2009 version of the tools, it appears to be working fine but will only show 1 of the 4 viewports at a time, even if I tell it to reset the 4 viewport windows. Some of the keyboard shortcuts (cut/paste for example, and tool hotkeys) are either not working at all or working with a weird delay, while others work perfectly fine!
Think I might build an entry in UDK instead...