Are you shutting down all non-essential programs before starting the game? (anti-virus, anything network related [even voice chat, at least long enough to see if that makes a difference], etc)
I'm not sure there is much locally that would contribute to disconnects...
If you are using a wifi connection, you could try wired, if available.
Try connecting directly to the modem, or if the system is connected to a switch, try connecting to the router (if cable lengths and the physical configuration allows).
Have you tried playing at different times of the day, to see if network load may be part of the problem?
Have either of you tried playing with anyone else?
