You can use javascript to use a different stylesheet but it's more complicated than using a conditional comment.
You should get your page working properly in Firefox first as that is probably the most standards-compliant browser. Then use a conditional comment in the head section with different styles for IE6 or IE7. These don't use javascript.
See http://www.wickham43.supanet.com/tut...tionalcomments
You can also use a completely different stylesheet for IE browsers using the above method if you have lots of different styles to edit or if you want a completely different color scheme, but it can only distinguish between any IE browser and the others, not between say Opera and Safari.
If you want to use javascript, look at
http://webdesign.about.com/library/weekly/aa123101a.htm
and
http://webdesign.about.com/library/weekly/aa123101b.htm
(it's a bit ut of date and I haven't tried it. You can use the same method for IE6 and IE7).
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.