To Have "No Clipping" During Game Play. You will need to 
edit your "autoexec.cfg" file. Use a Text Editor (i.e notepad). 
Change the "PlayerClip" "0" entry to "PlayerClip" "1". 
Just remember that you cann't Turn any of these off until you 
change it in the .cfg file. 

Also you can Have God Mode on. Just Change the "PlayerTakeDamage"
"1" entry to "PlayerTakeDamage" "0".