I didn't make it!
I have found on google that the newest version of GTKRadiant (1.5.0) supports HL2 based games like HL2, HL2DM, CSS etc.
Unfortunately this was all I could find. I haven't find anything if someone actually managed to get this to work, so i'm opening this topic here in the hope someone here has actually managed to get these games working in 1.5.0.
I would like to map for hl2, but have only mapped in GTKRadiant 1.4.0 for years, so i'm very unexperienced with Hammer and think I have a good head start with mapping for these kind of games when it is supported in GTKRadiant.
If anyone here has got this to work please tell me how.