Thanks folks! I used the remover, and it seems to work. There is no longer SecuROM entries on my registry.
Well, as for the game itself, I eventually found my original GTA 1 CD, and got rid myself of the collector edition. Now I have the GTA I'm already familiar with - the one with GTAFX.EXE in GTADOS folder. Tested it with DOSBOX ykhwong
I'm using September 2011 built
(20110922.7z), because the latest built crashes when loading state (IIRC because Taewoong uses Visual Studio C compiler). The 20110922 built can save and load state in Grand Theft Auto without crashing, but after loading state, the textures become corrupted that my car looks like a piece of sidewalk, building roof look llike mosaic of cars, etc, etc, and sometimes it's bad enough that it hampers gameplay.
Too bad. The reason I didn't finish GTA1 on the first place is because it cannot save a game during a mission - which could take hours. This game really screams for a save game feature.
I'll try tinkering with it again next weekend. Maybe the texture corruption happens because I'm using "dynamic" values for every parameter (automatic CPU cycle, changing DOSBOX output from Direct3D to OpenGL back and forth, etc). I'll try to run DOSBOX traditionally, with a conf file where everything is set statically, and try save and load state with GTA.
But otherwise, everything is fine. I'm using it with nGLide wrapper, setting max FSAA, etc, and the graphic looks great. Too bad there the save and load state doesn't work well with GTA 1.