I was having a long look at this... it is very doable, and should not be too hard to integrate - you only need to change a few lines of code here and there...
However, phpRPG is still BETA, and has lots of bugs. It's really a pre-released multiplayer RPG game based on php and mysql, and actually looks quite bad at the moment...
Also, the bugs are bad enough that you wouldn't want to use it anyway.
Refer to this review:
http://multiplayer.com/cgi-local/review.cgi?ID=1503
I would wait until they release an alpha version (it's still labeled as pre-alpha), at least a version 1.0 (it just became 0.5 from 0.3).