It's as simple as it is annoying. You get a high ID if your port 4662 is accessible (I believe you can change this to another port as well in the prefs), otherwise you're stuck with lowID. If you connect directly to the net, you should always have a highID unless you have a firewall on your computer. If you're on a shared line (home network etc), you'll probably have a lowID.
I've got that!
And yeah it's great... for downloading music!
But for software and videos it is total crap! There's alot of freaks on kazaa who rename their files... so you are never sure if you get the right file.