Buy a program to make a mod? Fairly expensive? Nonsense! twain088 wants to know how to make a Half-Life mod folder! (I guess)
http://collective.valve-erc.com/index.php?go=howto_modThat covers some things about the liblist file. The stuff about contacting Valve and so isn't important to you I guess...
In fact, all that has to be done is creating a folder with your mods name in your Half-Life folder, so you have Half-Lifemymodsname Then place a liblist.gam file in that folder, modify it and then you can either play it by choosing the mod in the custom game menu, or by adding -mymodname to your Half-Life shortcut.