I feel a bit DUH! But if you go into the options screen and click on the keyboard tab, you will then be able to click on the 'advanced' tab which is now highlighted, after this two boxes appear, tick the one that says Enable developer console (~), then click apply, then ok. When you hit the 'tilde' key during gameplay the console will then appear. Type in 'sv_cheat 1' and then whatever cheat you require, eg, 'buddha' (never die) ect. Hope this helps. Ju X (This cheat also works for episode 2)
Cheat Mode: Open Steam, go to your "Play Games" menu, and select Half-Life 2: Episode One. Right click on it and select "Properties". Click the "Launch Options" button then type -console. Click "Ok", then close. Double click "Half-Life 2: Episode One" to start the game. Once it is loaded and you are playing, press ~ to display the console window. Then, enter sv_cheats 1 and press [Enter] to enable cheat mode. You can now enter the following codes at the console window. Also, any code can be used as a command line parameter by prefixing it with the "-" character. Note: For games that were downloaded from Steam, to use cheats in single player mode, start the game with the -applaunch -dev -tconsole command line parameter.
Effect - Code God mode (server only) - god Spawn indicated item - give Reduce your health - buddha Damage player - hurtme All weapons - impulse 101 Ignored by NPCs - notarget Walk through objects (server only) - noclip List maps - maps Load indicated map - map