Why is the internet very slow?

[Plootahead]

The internet café that I used to go to had windows xp on their computers. I used to go there regularly, especially because all the computers had headphones making it easy to go on sites like youtube. But it closed recently(don't know why) and the internet cafés that are there now all have vista and mozilla firefox. But after a few minutes(sometimes seconds) of browsing, all of a sudden the internet gets very slow and sites take ages to load. This is really frustrating if I'm pressed for time or trying to watch something on youtube or even doing a search. Sometimes it's as bad as dialup! Why is the internet so slow in these places with the latest software and computers?