If you have Windows Updates activated, it should already have automatically downloaded and updated your system. To check if you have the patch installed, go to Start-->Control Panel-->Add/Remove Programs. Scroll down to the bottom of this list, and in the section for Windows Updates look for a "Security Update" with the identifier "KB960714". If you've got it, you're ok.
there isn't a problem with IE8 ... it's still in beta .. and therefore it's still in testing phase.
so no ... unless you know what you are doing ... and don't mind re-building your system if necessary - you shouldn't install 8 untill its a full release.