ya but he/she probable wants to get involved so don't discourage them,
when you finally know what your doing its rather fun--but long hours of testing and stuff-- so what you need is a "Half-Life SDK Pack" (Just Google it) and make sure you back up the original half-life dll... you will also need a C+compiler Im not sure where you would get this online-- I just bought mine and Indigo Bookstore for $59.99 but you can probable download a different version for free online--do take into consideration that if your just starting I'd buy it because it comes with a book to help you along the way----
I know I tried avoiding buying it, but after i downloaded a different version It was clear that I needed to buy it---although the version I tried downloaded only had the make.ini file and a bunch of other application files soo yep.... anyways good luck with coding---oh and when reading the tuts on coding be very* careful. Wrong coding could cause a disaster..
On that note Happy Coding,
"Only code If you absolutely need to"