Most people find IE7 a little difficult to use initially - people were used to IE6, which looked same as IE5, similar to IE4 etc...
Personally, I prefer IE7 to IE6, but the fact Shift-Click opens a new IE window rather than new tab is annoying sometimes.
Normally, I would recommend IE7, but I know your resistance to Vista which I suspect is mostly because its different, so not sure I can recommend to you to have ie7.
I'm sure you have friends/family already using it, might be worth having a look first, as I'm pretty certain IE7 cannot be cleanly removed.
Firefox is an option and will coexist with IE and other browsers, but remember it increases your attack surface, and Firefox has a very poor security history, so always ensure you keep it absolutely up to date (3.0.4 at time of writing).
Whilst on the Firefox rant - just under 25% of OOF's Firefox users are NOT using the latest version. FF users, not currently on the latest (or the later betas), UPGRADE NOW!