I've got a 22" monitor too (LG L226WTQ LCD) and that has a response time of 2ms - it works fine in gaming. I've just been playing Fallout 3 on it and it looks fantastic
If gaming is the main purpose of your monitor then I'd be sure to get one with as low a response time as you can. There are plenty of 2ms 24" monitors out there, so they may be a better choice than a 5ms one.