Can I use if lt IE9 in conjunction with if IE 8, in this manner:
<!--[if lt IE 9]><script src="html5shiv.js"></script><![endif]-->
<!--[if IE 8 ]> <html class="ie8"> <![endif]-->
I'm asking since the second condition is contained in the first one, maybe this could cause some glitch in one of the browsers?
Yes it should work fine, and the order doesn't matter, ie will parse all the rules and execute any that matches