The maximum resolution for both TV's is 1920 x 1080 if they are both "1080P" televisions. Both will work fine for gaming, but if you are going to sit fairly close to the TV/Monitor, then I would suggest the 32" because the pixels won't be as obvious as the 42". The 42" would best suit you sitting further away from it (like a couch to an entertainment center distance).
Also, for gaming, I would definitely recommend getting a television that is 120hz. I have a 47" 1080P HDTV that is 60hz and it doesn't look as good as it does on my monitor. Many people here on the forums have clarified that the 120hz TV's make all the difference but in the end both will work.
Oh, and don't forget to get a DVI to HDMI adapter.