comon, half-life is usually only 5 bucks at the nearest software retailer, its really worth buying it,
1) halflife 1, a real classic game, its fun!
2) steam, its rox0rs the big oneone... at least that is what they want you to believe but you can download it at those links the others gave you,
3) ESF, aka Earth Special Forces, best DBZ mod for half-life out there, IMO even the best Half-Life mod there is, you download it from esf-world or another mirror, you install it and tataa.... your playing one of the best mods there are, and it only costed you 5 bucks.
Not everything is free, and we don't force you to play ESF, if you don't want to play this game, if you want to miss the oportunity to play one of the best mods out there... well then you just do that.
I mean, 5 bucks isn't that much, (unless you live allone, have to pay for the rent, food, bills and everything, then it might be to much).
This thread has answered your question, don't moan about having to pay for games please, it's downright rude.
Also, it could be considered warez if you ask specifics - and to prevent this I am closing the thread.