Realy weird lag Q3A Multi

[TaTiNaToR]

I'm constantly running 90FPS in both single and multi player games and I have 6.3Mbs broadband wired LAN, but I am still getting lag in multi player.
Not the usual jerky type of lag either, it's constant like I'm running almost half a second behind the game. I go to shoot someone and they aren't there, I can be running down a corridor and get shot and not see the person who shot me untill a fracton of a second afterwards. Also when I am spectating I can be watching someone and they could shoot another player but the player is nowhere near where they have shot.
It's realy weird, I have had slow systems and internet in the past and suffered some monster lag, but this is just realy realy weird.
My system
Athlon 7750 Black Edition @ 3.0Ghz
Asus M3N-WS
Akasa Evo Blue
2Gb OCZ SLI 1066
Onboard 512 shared Nvidia GeForce 8200
2x160Gb Maxtor Raid0 Striped
450W I-Cute PSU

I have configured both the firewall and the router for Q3A, and the internet is Constant 6.3Mbs, but it makes no difference if I disable the system and router firewalls.
I have the demo game BTW

[^misantropia^]

- Virus scanner / other background applications?
- Is the lag constant or every now and then?
- Does it happen on all servers?
- What is your in-game ping like?

[TaTiNaToR]

I have managed to improve the lag a little by increasing the screen res to 1024x768 32bit. But it is still noticable.
Nothing much running in the way of procceses, well nothing the dual core can't handle, I'm still getting the full 90fps at the higher screen res. Ping is below 70 on most of the servers I visit. I recon it could be an open GL problem. I will make sure I have the latest DX and post back.....