How to make those sweet backgrounds???

OK, on a lot of high-quality CSS sites they have these really cool backgrounds that almost look like fabric. My question is how do they make them? Is there a tutorial out there that anybody knows of? I know how to make seamless backgrounds in PS but not as cool as these. Here are some links to show you what I'm talking about:

http://www.7nights.com/asterisk/
http://www.csszengarden.com/?cssfile=085%2F085%2Ecss
http://www.whatdoiknow.org/

There are a lot more out there but I can't remember the urls. The one I like the most out of those links is the first one.

Anybody have any info or tips???

Thanks everyone.