Arighty, I map with Hammer for Steam 1.6. IT AINT EASY!! First, I used this link
http://www.egir.dk/index.php?page=vhe_setup.htm here for most of the Hammer setup BUT it doesn't work all the way. I ended up finding the halflife.wad in my Half Life Dedicated Server folder, for one. The main workaround I have to do is that setting up according to the link aforementioned, the .MAP ends up in the right place, but the .BSP and any other files end up in my C:Program FilesSteamSteamApps folder, with the name
myemail@myemailserver.bsp etc. Also, I use Hammer 3.5 BETA which works, but I had to switch the file to READ-ONLY because it kept regressing to Hammer 3.4 for no good reason. Also, I had to put the halflife-cs_expert.fgd (FilePlanet or somewhere) in the fgd folder. ALSO, File->Run in Hammer 3.5, at least for me (who has Blue Shift retail, no cstrike.exe anywhere), does everything it's supposed to but gives you an error when it runs tries to run your level. This is actually pretty handy, because it means my machine
bleeps when it's done compiling. Then, I just have to rename and move my .bsp and run steam. Good luck!!!