atmays, download WinMTR off
http://winmtr.sourceforge.net/winmtr_bin.zip and set it going using the IP of one of the servers you have the trouble with. The program basically just pings and traceroute's the target IP until you stop it. Leave it going for a while and paste the results on here so we can have a look at it - Hopefully this should tell us if there is congestion or packet loss between you and the servers, and what part of the route is causing the problem. If everything seems ok, I can only assume it is your PC and possibly some firewall software on it.
After looking at your demo, you seem to be getting intermittent solid white bars whenever you experience lag, and a very low graph all other times, which I
think means packets are being delayed heavily, but not lost (which i think would produce a black line). The WinMTR should show us if any routers on the way are heavily congested.
On the other hand, I once had the strange side effect on my own connection of my ISP's CoS measures that would hold back UDP traffic at busy times if it couldn't recognise the type of traffic. Pretty crazy policy really, given UDP is usually used for real-time delay-sensitive applications! If this is the case with you, there isn't much you can do other than see if their system learns about the game traffic, or send them a letter saying you're annoyed or something.
Good luck,
Dagless
