Found this on another forum I use. It works for me and speeds it up no end.
This piece of software which establishes five connections to youtube and sends them to you and unpacks them.
It really works, at first it doesn't look like it but after about 10 seconds the video starts loading really quickly!!
Anyway don't forget to untick the boxes which want to put rubish in your toolbars etc. And you don't have to put your email address into it (it says optional)
Anyway here is the link and it is free
http://www.speedbit.com/video%5Faccelerator/
PS Do run it through you virus checker and obviously i can't take responsibility if it contains anything dodgy.