AgentMomo wrote:sounds like something i would like to try doing then ,
What tools would I need ?
First off you need the original Half-Life for PC. Not the current fancy one on steam - the one which came out on discs in '98 (to make sure you have the lowest version possible). Then you should start looking for programs like Photoshop/Gimp (graphic edit), Milkshape (3D modeling and animations), WorldCraft/Hammer (mapping), PAKexplorer (to open and save PAK container), Audacity (sounds and music), a text editor like Atom/Notepad++ (to script some stuff and change cfg files), BootDreams (.cdi image creator) and a working Dreamcast emulator (nullDC e.g.)... BUT because of the missing WinCE support you can't test it on an emulator. So you must burn every single version of your attempt on a cd-r, walk to your Dreamcast and boot the "build" on real hardward. Otherwise you can't test your results.
If you want to port content over to Half-Life make sure you have the right plugins and tools to open/extract/encrypt/change/modify/save this other content.
But the most important aspects for this endeavour are: a LOT of spare time, patience and dedication.
These are just some programs that came into my mind while writing down this text. I'm pretty sure there are easier or more modern tools for the tasks. But I used them some time ago (and few still today) for my own projects and can confirm that they will do the job.