A product called OOOP! and Good-bye Splatters will supposedly remove dried latex paint from brick (among other things.) I can't vouch as to their effectiveness though. You can visit your local Paint Retailer (found in the YELLOW PAGES under 'PAINT - RETAIL'.) They might be able to help you.
This is a job you may regret once you start. It is difficult and tedious to do because of all the nooks-and-crannies that comes with brick. One product, though, that has produced good results per 'others' on this forum is PEEL AWAY. It may be worth a try.