This is the first time attempting to validate a site so I apologize if the lingo is off!

I went to The W3C Markup Validation Service to validate my homepage and it's not happy with my superfish generated menu (You can view my site in-development at www.myalgebrabook.com username: a password: a). I've tried adding in another <ul> tag but then the menu doesn't work. So, as a newbie to "site-validation",

1. Does it really matter if my navigation menu doesn't validate properly?
2. Any thoughts as to how to address this particular issue?
3. A CSS person on this forum suggested that I was a bit crazy for using javascript for the menu and that CSS would be much better. Your two cents?