I guess Youtube, as almost every tutorial is hosted there :)
If you mean Web designing, you'll don't need a lot of computer power to do some basis things.. For HTML you can use either a WYSIWYG (dreamweaver) or a notepad(notepad++).
For the real 'designer'-part, you'll probably going to use Photoshop.
I'd say, for system requirements: an Intel core i3, 4Gb of RAM and a basic video card will do the job :)
