For a great primer on scraping see this pycon 2010 conference video by Asheesh Laroia ..

http://python.mirocommunity.org/video/1616/pycon-2010-scrape-the-web-stra

it prety much covers everything we have done...

If you are already familliar with the technicalities of http and how it can transfer state then half of the presentation will be unnecessary

If you are also fammiliar with mechanize or urllib2 and beautifulSoup, then 90% of the video will be old news.