If you do install as I have done and do not like it the uninstall will roll it back to IE6.
Two things to think about, it does not like out of date add in toolbars like google or yellow pages. So either go to the sites and update them or uninstall before you do IE7. You can always add them later if you wish.
Are you on BT or NTL broadband if so there is something else to consider but its not serious I promise. IE7 is excellent in my view the tabbed browsing is really useful.