steam should automatically patch the game for you. I have the game (not my favorite to say the least, it's 'ok', i guess) and haven't had any such issue. I cant confirm worseelite's conclusion, but it seems to be the most logical action. Another option, would be to open steam, rightclick on the DM icon, and open options. Then find a button called "Set launch options", and add '-dx9' (without quotes), and hit 'Ok'. That seems to fix most display issues with source engine games.. I know HL2, and CS:s need that to run right on my system.