I want to factory reset my nortel AP 7220, how do I reset? What would be default IP after reset?

AP7220 has a CLI. To access the CLI you Telnet to the IP Address of the AP7220.
If the AP7220 has a default config, the default IP address is 192.16810.2.
To configure a AP7220 with default config connect your PC to the AP with a crossover cable, and set the PC IP address to 192.168.10.1.
Telnet to the AP and enter the userid and password for the AP (default is admin/admin).

Enter "?" at the CLI prompt for a list of commands. Should be a reset command there.

There is probably a reset button somewhere on the device, it is probably a small pinhole that you put a paper-clip into the reset.
If it has its own http web page, there is likely a reset to factory defualts option.

The ip of the computer connecting to it should not change.
On a computer connected to it, open cmd start>run then type in cmd, and type 'ipconfig'.
It will display details about your connection. Where it says 'default gateway' is the ip of the device.
You could try to put the ip in your browser and see if the device has a web page.