IE version

Question

Hi
I have a website that works fine with IE 7 but now I am using windows 7 along with IE 8.
when I build my website in visual studio it automatically runs it with IE 8(the only IE I have).
I tried pressing F12 and using Document Mode:IE 7 option but this change will not remain after the next run of IE 8.
how can I make that change permanent?
or any other solutions please.