yes u can, u can connect to yaself on the internet using you net IP address, or you can connect without going on the internet thru the loopback address 127.0.0.1
i have done this to test my own code and it works well enuff, what you need to do tho is to run ya game in windowed mode tho and switch between the windows, the drawback is ya system slows down with more than one instance of the program running. i have had up to 6 windows open like this (on both methods, thru the net or thru loopback) and besides the slowdown (which might just be my junk pc!) there were no problems
optic blast! megablast! have a blast!!