Speeds slow and then pickup on reconnect

[#1]

My connection (8 mbit) has a reasonable speed if I reset my router, but then gradually slows down to about 500kbps. Could this be a problem with my router (just updated the firmware and erased all config settings and re-configured), my comp or maybe the connection. Any ideas anyone?

[#2]

It's a netgear wireless ADSL firewall router DG824G. I connect to the net with my router and then wirelessly from my comp to the router. My OS is vista. It's not a problem with comms between comp and router, I'm sure of that. As for stats, as I said in my first post I just wiped everything so I don't have any.

[#3]

The line stats should be available as soon as it rebooted and connected.
Its the line attenuation and SNR/Margin for both up and down we need.