ADSL Drop out

My ADSL connection keeps dropping out every 20 seconds or so since I
bought a new D-LINK DSL 300-T modem and linksys wrt54g wireless
router. It must be a problem either with the router or combination of
the 2 as this doesn't happen when I use the modem on its own.

When I try to ping somewhere with the router attached I get the
following:


Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=14ms TTL=250
Reply from 212.58.224.56: bytes=32 time=14ms TTL=250
Reply from 212.58.224.56: bytes=32 time=16ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Reply from 212.58.224.56: bytes=32 time=298ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=14ms TTL=250
Reply from 212.58.224.56: bytes=32 time=17ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=14ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=20ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=14ms TTL=250
Reply from 212.58.224.56: bytes=32 time=14ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=14ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Reply from 212.58.224.56: bytes=32 time=18ms TTL=250
Reply from 212.58.224.56: bytes=32 time=15ms TTL=250
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Reply from 212.58.224.56: bytes=32 time=969ms TTL=250

etc

Ping statistics for 212.58.224.56:
Packets: Sent = 1744, Received = 1347, Lost = 397 (22% loss),
Approximate round trip times in milli-seconds:
Minimum = 13ms, Maximum = 3013ms, Average = 44ms

Any ideas what setting on the router could cause this?