Monitor doesn't impact performance per say, but it does impact how you see the games a lot.
Many of the "gaming" LCD's out there use 6-bit panels, meaning they only display 6 bits of colour depth rather than 8 bits, and they dither to get the rest.. basically doesn't look as nice IMO.
Different panels use different technology as well, and some inherently look better than others. And of course screen makers don't share this info very easily, so it can be tough to find a truely good monitor.
Mind you maybe I'm just too picky. 90% of people would probably never know the difference.
For the 226BW, it looks like it's good for gaming, but it's colour accuracy isn't the best.. but that's not usually a problem for most people (ie not doing graphics work on it).
From a review:
http://www.xbitlabs.com/articles/oth..._12.html#sect0