FFT:
Answers are volunteered. If someone can help, they will.
Based upon X-cart's complexity, I would strongly suggest finding the answer from one of X-cart's 3rs party vendors. Unless you're a programmer, or at least REALLY FAMILIAR with X-cart internally, leave it to the pros and purchase a solution from one of them.
Here's a list of 3rd party companies that provide all kinds of mods:
http://forum.x-cart.com/showthread.php?t=37649
I'm sure one (or more) of them have Facebook and social networking mods for X-cart.