Like johnpalmer, new tabs always open as blank for me. It's only the first page I open which opens as my home page.
To be honest, I've always assumed that's the way IE7 is supposed to work - every new tab opens as a blank unless you've used the middle mouse button to click on a hyperlink - in which case a new tab opens for that hyperlink.
I'm not sure now that I am understanding correctly. First I have 4 sites listed as my Home Page in IE Options, so when I open IE all 4 of those pages open in separate Tabs. Second I have "Links" Enabled in the Menu Bar over the tabs. I have about 10 different links listed there and if I click on any one link it opens a new tab showing that particular link. I hope that is clear, I am using IE 7, but it also worked in IE 8 when I tried it.