Things to keep in mind while web designing for ie 6 and ie 7

Question

I have just started doing webdesigning I use photoshop and dreamweaver. I have seen that professional websites carry different css for ie 6 and ie 7 and one for all others. Why?
what are the different things I should keep in mind while designing for internet explorer 6 and 7 and how is it different from designing for other web browsers. Are there any other web browsers that like ie 6 or 7 which require different css ??
can you give a link where i can read more about it

Answer 1

basically internet explorer renders websites differently in a bad way. internet explorer 6, 7, 8 all have their little quirks. For the most part other browsers like opera, firefox and safari render sites in a similar fashion.

then main gripe is that internet explorer has a different box model. you can read about common issues with IE here:

http://css-tricks.com/482-ie-css-bugs-thatll-get-you-every-time/

http://haslayout.net/css/

there are however lots of scripts/tools that can help you out:

http://code.google.com/p/ie7-js/

http://www.findmebyip.com/litmus/#target-selector

on a side note please don't support ie6, it is by far the worst browser to work with and many companies have stopped supporting it.