This may sound like basic info to some, but others may need it
If you have a firewall other than Windows Firewall, go into start / settings/ control panel/ administrative tools / services and make sure windows firewall isnt running at the same time as your other is. When I stopped the windows firewall process the lag reduced alot (Don't turn it off if its the only firewall you have)
Also if you can, reduce your current firewall/AV to run only the neccesary components while you're playing and turn off other unneccesary services. I turn off the web based stuff if im just in the game.
Black Viper still has a guide for which vista services are neccesary and which arent, that I've found really useful in freeing up resources.
Just be sure to do a start/programs/accessories/system tools/system restore and create a restore point just in case you get confused and forget what you had on/off if you have problems and want to go back to before you began fiddling with it.
Now Im going to get back to trying to get mine working properly (right now I cant get lists of games available in multiplayer.. the green stuff)