It's remarkably simple to use a Bluetooth keyboard with the iPad. First, you just need to ensure that your keyboard supports HID mode, that's Human Interface Device Profile and is pretty much the closest thing to a universal Bluetooth keyboard interface out there these days.
You simply need to put your keyboard into pairing mode, go to Settings -> General -> Bluetooth on the iPad, and then tap the keyboard's entry. Then the iPad will pop up a message with a pairing code you need to enter into the keyboard. Once that's done, you're all set. Now when you come to a text entry field, instead of the on-screen keyboard popping up on the iPad, you simply enter text on your Bluetooth keyboard.
I used the Freedom Universal Bluetooth Keyboard, which is available in the TiPb iPad Accessory Store for $99.95. If you order before April 14th, you can enter coupon code iPad10 to get 10% off.