Tethering the Wi-fi iPad to Your 3G iPhone Without Jailbreaking
Important: these instructions are theoretical. I don't (yet) have an iPad. Also, these instructions will disconnect your laptop from any wi-fi networks it's connected to.
iPhone 3G or 3GS
Assumptions (tested on):
Operating system: Mac OSX 10.6 Snow Leopard
Laptop: MacBook Pro
Canada, where Fido and Rogers offer 3G tethering to customers with a 1 GB+ data plan
Not tested with an actual iPad, but was able to connect to the wi-fi network with a second laptop's AirPort.
Tether your iPhone as you normally would. This works for both USB and Bluetooth tethering.
On your MacBook Pro:
turn on your Airport if not on already
click the Airport icon in the menu bar, and then Create network...
give your network a name, and assign it a password
for Security:, select 40-bit WEP (more compatible).
Click the Apple icon in the top left of your laptop's window, then System Preferences...
Click the Sharing icon
Check the Internet Sharing checkbox
In Share your connection from:, select the tethering port. This will be something like Ethernet (en7)
In To computers using:, select Airport
On your iPad, connect to the wi-fi network that you created in step #2 sub-step #3.