Goto System->Administration->Software Sources
Enable all software repositories under the Ubuntu Software and Third Party Software tabs.
Now, at a terminal, type in:
sudo apt-get install wine
Install the Wine gecko engine
At a terminal, type in:
wine iexplore http://www.google.com
You will be prompted to install the gecko engine. Proceed with the installation.
Install Counter Strike 1.6
Proceed with the installation of your Counter Strike 1.6 (CS/CZ).
Now goto Applications->Wine->Browse C:\ Drive. Open Program Files->Valve->cstrike.
Now locate the files: download.htm and motd_temp.htm
For each of them, right click, Properties->Permissions and uncheck write permissions for your username (ie. mark them as read only).
Finally, execute the game, buy an m4 and give some headshots!