I just have one quick question. Is there any way to play these games offline, alone, by yourself??

Thanks

There are ways to get very braindead bots in the game, but otherwise - no.

The Quake 3 versions (Q3TC) have bots included in the game for single player/offline action.

The Enemy Territory ones don't (normally. I believe you would need to do some fiddling to get them to work).

Thanks

Its possible to play with bots [offline]
Anything You need is a waypoints folder for bots, and specific config.
If You wanna try, send me pm and i will give You all needed files and txt tutorial how to create server with computer players.