(Theme: Swift Basic) Issues in rendering in IE 7 and IE 8

Hi,

Cross-browser testing my website http://www.ottimizzazione-pc.it/ I noticed that there are issues in its rendering in IE 7 and IE 8 (all the other browsers and versions seem fine).
The problem seems to be the top menu: all the sub-menu lines in the dropdown menu are displayed, this obviously takes a lot of space, and to get to the actual posts users are forced to scroll down a lot!
My theme is swift basic and I don’t have support from the designer (it’s for premium customers only), so would you have an idea of what’s wrong and what I should do to have the website displayed properly?
Thanks for your help