In short:

My ping is 50ish and I lag like hell. Happens even when I log in right after reset and when there's like 10 people online. I asked some other people and they're not experiencing any lag at all. This didn't happen before when I used my original CD's to install the game but since I no longer have a CD/DVD-ROM I had to download the game. I got the Diamond Edition from GOG and replaced the cd keys with my own.

Other info:

Win 7 64bit
Nvidia GeForce GTX 580
I use Direct Connect and I run it in compatibility mode (Win XP Service Pack 2) with disabled Visual Themes and Desktop Composition. Also I run it as admin.

Any ideas what's wrong? Or how to fix it?

Thanks