Speedtouch 780 - LAN gaming problems

Hi

I've had a long look through various forums here and can't find an answer to my question ... apologies if it IS a duplicate.

I'm running an O2 wireless box (Speedtouch ST780WL running software 6.2.27.2) and have my Vista Home PC connected via ethernet. My son's PC is running XP Pro and is connected to the ST780WL by an 802.11g wireless connection.

I'm having problems with LAN gaming on this setup - although I can get the two machines to see each other the connection is far from reliable. When playing first person shooters (BF2) and real time strategy (C&C 3) I find that there is a lag spike at regular and frequent intervals (about once per minute). Additionally, either PC will sometimes drop the connection and then won't refresh the server lists without restrating the game (regardless of the game we're playing). Note that we have tried hosting games on both PCs and the result is still the same.

I've tried 3 different wireless adapters on the XP machine (one internal, two USB) and the problem persists. The wireless PC is about 15 feet from the router and frequently has line of sight to it so I don't think it's a dodgy wireless connection.

I've also connected both PCs by ethernet and things are much better the ... but having both wired up is impractical given that we normally use our machines in different parts of the house.

Is there a known problem with the wired/wireless bridge on the 780?