No problem
I wouldn't recommend that one because XHTML 1.0 Strict is at the top end of xhtml coding and is very picky about the way its used. The code in your site is xhtml so I'd recommend...
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
Transitional is a bridge between the older html and the new xhtml, and its a lot easier to use than
strict.
You may want to read to get a better idea of the differences. Also try searching google for
and you'll find many other articles explaining the differences.
Once you've put that doctype in to the page you should be able to validate the page using the helping you to find problems much easier.
Oh and before I go you should check out which has examples of common IE css bugs and explains how to solve them.
Hope that helps.