Before we get the "avoid IE8 like the plague" brigade I'll just chip and and say that if you're using IE7 it's probably more a security risk than IE8. There's a few more features and has been OK security wise for me at least (I tend to use it as I can't be bothered with much else though I have installed Firefox recently purely for the Firebug CSS add-on)
If you want it on your other PC just go to
www.microsoft.com/uk/IE8