Hopefully, someone involved with this can give you more info, but until then you might try -
http://www.christianitytoday.com/yc/2000/003/1.10.html
Also, try Googling [video transmitter (broadcast quality) church services] and see if you don't get some good links.
Just an idea - assuming you mean transmitting the signal to a receiver elsewhere within the building and not an uplink - since you only have one location (the church), why not cable it instead of transmitting? That might be cheaper and avoid interference problems, etc.