Philips SNA6500 Wireless + Virgin

Hi, recently got my wireless network sorted, working off the above titled router, and two laptops with wireless capabilities. It was actually relatively simple to acheive in the end, however ive run into a problem i expect a few users get. My connection periodically cuts out.
What occurs is the ADSL light and On-line lights go out on the router, and the wireless connection indicator in the task bar goes to disconnected. Withing 30 seconds the router has reconnected to the ADSL and gone 'on-line' and everything is fine again. This is a bit of an inconvenience when using MSN messenger or uploading/downloading. What could this be?
Detaisl: Philips SNA6500 Wireless Modem Router, Ralink RT2500 Wireless card (in laptop), connected to Virgin ISP.
Any suggestions would be great, thanks