AFAIK Internet2 is one of those "discussion" organizations that exists just so important parties can coordinate their efforts... they don't actually do anything themselves.
There are a couple high-speed networks that have been up for a while now... Abilene (this is somehow related to Internet2) and vBNS, others. They only link up universities, big corporations, etc though. When I lived on-campus, we were linked into the school network and got vBNS connectivity -- downloading files from MIT or something sometimes went so fast that they saturated the local 10Mbs Ethernet.
Does anyone konw how it works that gives it such great transfer speeds?
Well, your usual DSL/cable/modem is just the part of the connection you use to get to your local ISP. They usually have direct links into the Internet backbone(s): high-speed, high-bandwidth fiberoptic (OCx) links connecting major nodes (PoPs).
Back in the day, there were just a few backbones -- UUNet, Sprint, etc -- that mainly interlinked at two points, MAE West

and MAE East. Anyone else remember those days?... now it's much more complicated. Anyways, the big thing about these superfast networks are:
- They use newer, better fiber-optic cable links -- the main issue is with repeaters, since they run at electronic vs light speeds. The recent test was over OC-192, but they've developed up to OC-768 now. The OC-# is in multiples of 50 megabits/second.
- They use crazy fast and powerful routers, and effectively optimizie traffic.
It's pretty cool stuff... you can check out Abilene and vBNS network maps:
[Removed Broken Link]
http://abilene.internet2.edu/
and look up terms above to find out more. :)