I'm no expert on Sky Broadband but I believe the speed they give should be plenty fast enough for you watch video. The problem may be memory or simply the age of your PC and it's components.
Going back to the memory check. When you get the "whole lot of numbers" come up in the Physical Memory box it means:-
My figures now for example:-
Total: 2088316, which means I have 2GB of memory installed.
Available: 1133436, which means I'm using about half my available memory at the moment, i.e. 1.13GB.
If your available figure is low then you will not have much memory installed. scotman's instructions tell you how to check how much physical memory you have installed, mine tell you how much you are using and how much you have spare.
To check your Broadband speed go to this website and click "Start Speed Test"
http://www.broadbandspeedchecker.co.uk/