If it is running ok in IE7 and you want it to run similar to IE7 in IE8 as well then,
write this below <title></title>
<meta http-equiv="X-UA-Compatible" content="IE=7" />
There can be some other issue like wht property are you using in css because of that it behave diffrent in diffrent browser.
and for Resolution,i think you hv to design pages in %.