I do not have a betta myself but someone gave my mom one for her desk at work so i looked up some information for her. This is the site that my mom said was the most useful to her. Figured I would post this since there seem to be a lot of questions concerning betta's recently.
betta's are the most low maintanence fish you could get... they can not stand cold waters say like a carp or minow... they should be kept in a room where the temperature is stable or with a heater... i have 5 bettas together in a 25g planted tank...
i used to have wild bettas in 5g tanks... but i ended up giving them all away to make room for my bigger breeder tanks...