Odd behaviour since Netgear 834GT

Dear Experts - my reliable system, MSIK4, Athlon 2600, 512RAM, XP Pro,
2x80Gb Maxtors has started to display a few foibles since I installed a
wireless network. If anyone has any pointers, I would be gratefull to
receive them!
Oddities include...
Running Checkdisk at every startup but only on Drive D:
Screen freezes when downloading streaming video (usually French news,
Your Honour!) also BBC ClickonLine but not BBC "News" videos
Very slow running when loading any media players.

My Anti-Virus (CA EzArmor/Zone Alarm), Spybot and Ad Aware report no
malware and GRC "Shields Up" reports "Very secure" with no ports probed.
The wireless network has a 128 bit WEP key.
I have done two re-installs of Netgear firmware. The system works very
well when "directly" connected to the BT Voyager 105 BBand modem running
at (allegedly!) 2Mb.

TIA
David

--
Those who hear not the music think the dancers mad...