@Ministeve: Since Nem's site is not working, you really have to link directly to a GCFScape mirror -
http://rabidmonkey777.bluewolf72.com/files/gcfscape.zip is mine.
This utility will let you open the GCF files Steam stores game data in, major_righteous. (located in /steamapps) Make sure you have Steam closed (right-click - exit in teh tray) and open source sounds (I think) .gcf - This has the HL2 soundfiles. You can get an idea of how they're structured by looking at this (ie, foldernames.) Then, you can just recreate this structure with new folders in steamappshalf-life 2hl2sound.