The WiFly module will plug into a regular XBee shield, and can be configured
via the Arduino's RS232 port. You don't need an SPI port/shield.
However, it's easiest to setup the WiFly module parameters from a PC using the USB
port of the Arduino. To do this, you need an XBee shield that can swap the RX/TX pins.
You also will need to hold the Arduino in reset while configuring WiFly, so the Arduino
relinquishes the USB port.
Afterwards, you can setup an ad hoc network with the wifi on your PC, but will
need a UDP/TCP program such as ZOC, or other utility.