making a mod is VERY easy...
in your halflife directory, make a new directory like "mymod"
copy the file "liblist.gam" and the directory "dlls" from the valve folder to "mymod"
open it with notepad, you get to see:
// Valve Game Info file
// These are key/value pairs. Certain mods will use different settings.
//
game "Half-Life"
startmap "c0a0"
trainmap "t0a0"
mpentity "info_player_deathmatch"
gamedll "dlls\hl.dll"
gamedll_linux "dlls/hl_i386.so"
delete that text, and paste:
// Mymod Game Info file
game "my mod"
url_info "your mod's homepage url"
url_dl "your mods download url"
version "the date you finished ur mod.."
size "the mods size in bytes"
svonly "0"
cldll "0"
type "multiplayer_only"
nomodels "1"
gamedll "dlls\hl.dll"
now everything u put in the mod, will replace the standard of HL
so when u put in a map in the "maps" file, it will show up in the
create game menu..
if u make a "mymod\gfx\env\splash.BMP'', that will be the background of the main menu.. if you dont make that file, nothing changes..
you also need to put in "mymod\cl_dll\client.dll''
you can copy it from valve if you make a simple mod,
but if you want to make coding changes, you'll have to make one urself..
so if you want to learn coding:
www.planethalflife.com\hlprogramming
learn mapping:
www.valve-erc.com
i hoped that helped a little..