The great folks at the Widescreen Gaming Forum have a working solution for setting the correct FOV for 16:9 and 16:10 widescreen displays in Painkiller. This will allow you get an expanded field of view on widescreen displays instead of a zoomed and cropped image.
The solution involves changing two lines in the config.ini file, which is found at Program Files\GOG.com\Painkiller Black\Bin.

Thanks for info!
It is rather surprising that a game of 2005 can support widescreens, even today most of the new games(mostly MMOs) can't due to poor UI implementations etc.

I can't set my resolution above 640x480, even after setting the resolution in the config and changing the FOV settings.
Anyone know what's going on?
My specs are:
ATI 4850
E6600
XP 32-bit
LG monitor

This seems to happen to certain LCD monitors. This thread in the DreamCatcher forums (in particular, the last two posts) suggests uninstalling any utility software that came with your monitor.

Thanks for the tip! :)

Thanks man. I couldn't find the software for a while, but after a bit more detective work I ended up finding out I really did have some software, but it was called forte manager or something. So if anyone else out there has an LG LCD monitor that is what it is called.