Your other problem: I'd say you need, in the case of Hammer, the "change directory line". Say you're in c:Documents and Settings, and you type or run Half-Life (i.e. c:SierraHalf-Lifehl.exe), HL will then (with some OSes) load that EXE - and revert to c:Documents and Settings. Then it'll try and find c:Documents and Settingsgfx. You see the problem?
If you compile in Hammer, click "Expert" in the compile ("run") prompt window and check the lines that are there.
PS: I'd get out of the habit of carving. Half-Life is just as happy if you construct hallways out of seperate brushes manually, as long as all the edges meet up.