This is currently a problem with an unknown cause (AFAIK, anyone better informed feel free to correct me). Some games, Top Spin being one, start fine and then go green after intro videos etc. Some emulators, like Mame and Surreal64 also go green (on launching a game, IME). Apparently, some games that start off and stay green can be fixed by lauching them through XBMC/P.
As for NTSC or PAL, the only way the Xbox knows if it's a NTSC or PAL is a setting on the EEPROM. You can change this using the Enigmah video mode switcher, or theres an option on the X3 BIOS config thingy. To ouput a progressive scan signal (which a monitor requires), the Xbox must be set to NTSC. Yours must be set to NTSC for you to see anything on your monitor, so don't wory about that. I don't think it makes any difference for the games, all PAL games still can output progressive scan, if their NTSC version can.
The iND-BIOS 5001 VGA is generally regarded as the best VGA BIOS if you have a Conexant video encoder. It has useful features not in the PIxel8 or TATX BIOSes, which also are not confirmed to work on all versions of Conexant Xboxes. It also can output VGA over unmodded component cables, which is handy for people like me who have a sync on green monitor with BNC inputs for RGB, because all they neeed is the right cables/adapters with no modding required.
