Kelly_B,
I read somewhere a year or two ago that
TPWD was taking an active role in putting up bat houses in Texas parks. The bat's presence reduces the need for insecticides and other insect limiting/prevention methods.
stingrey,
Check out Bat Conservation International's bat house webpage. They've got a pdf containing bat house construction/installation instructions. There are also a couple of pdf's telling how to attract bats and the criteria for bat houses.
http://www.batcon.org/home/index.asp?idPage=47
BCI also publishes a very nice Bat House Builder's Handobook containing a variety of designs for different areas of the country. One thing that does seem to help in attracting bats to a bat house is to have a water course of some sort nearby (sandpit, pond, creek, bayou, river, maybe even a swimming pool--although I've never seen bats around my pool).
regards,
dale