ss.trunks,
If you have already installed steam, you can purchase half-life directly from them (if you have a credit card, or if you are a younger user, see if your parents would let you use theirs, I am pretty sure the game is only $10 or $15 directly from steam). This is probably the easiest way to go, it will download directly to your computer then. Then you will need to reinstall ESF mod.
And, welcome to the community.