you will have to Jailbreak your ipad and then purchase an app called iBluever from cydia and, also, put an app on your blackberry called PDANet (It's free)
The process is pretty straight forward, once you get those two apps installed, goto your bluetooth settings on blackberry and turn OFF "bluetooth dialup networking"
then
make sure the bluetooth on the iPad is OFF
launch PDANet, tell it to start bluetooth tethering or whatever the option says
then launch iBluever on iPad and refresh the little area to see the BlackBerry, then tap the BlackBerry that it sees, in the number, add #777 then there are two other options later that are like wait for blackberry or something and something else...sorry..but you want them both checked
then go back and it should connect
It's sort of slow, but its good in a pinch, only problem I had with it, is that sometimes it crashes, and you have to reboot the iPad to make it work again
cheers!