the archive and install does a clean install (but not an hd erase) and then takes all of the files from the origional install of osx (like preferences, apps, user documents, etc.) and puts them back where they belong. if you are sure that you don't need 9 for anything (if it's your first mac, you probably will not, i've been using them for about 8 years and don't need 9 anymore) just go ahead and do a format and install from the 10.2 disk (but if the computer came with any apps on it, make sure to burn them to a cd before you reformat). a format and install is the best option since you don't have any of your own work on the machine. it will be a much cleaner installation and you will not have to worry about compatability problems between 10.1 and 10.2 and you will not have classic to bog it down.