It seems we both decided to try modding with the Orange Box PS3 release at about the same time. The only tool I can think of that could modify or even view these files, the .GRP files found on the disk, is GSSMT (GoldSrc & Source Modding Tool, found on moddb), but unfortunately it only works on the OG Xbox release of Half-Life 2 and the PS2 release of Half-Life. I think there is some documentation on the Valve Dev. Wiki, but I'm not 100% sure if there are any tools listed there that can do this... yet.