Right .Easy way to play CSS with dxlevel_81:

Go to your Counter Strike Source folder ,create a shortcut for hl2.exe ,right click on created shortcut - Proprieties - at Target should look like this: \Counter Strike Source\hl2.exe"
add this at end -steam -novid -game cstrike -dxlevel 81 .Finally should look like this :
\Counter Strike Source\hl2.exe" -steam -novid -game cstrike -dxlevel 81

WITH SPACE AFTER \Counter Strike Source\hl2.exe"
HAPPY FRAGGING

Regards w4rkr4f7