no, do not format right away. first off, has the explorer been crashing ever since you installed w7? has it been crashing after an install of a new software or update? if it has been crashing ever since install, yes then a repair/reinstall would be in order. if not then you should try to think back to before it started to crashed and uninstall anything new, including browser toolbar add-ons one by one.
this was an issue with quite a few vista installs. i am actually currently experiencing/battling that with a customers (vista) pc. it was in his case a game which was causing the explorer window to crash. so removing it and then a reboot did solve the problem (for the moment at least). often time it could be a compatibility issue, esp since w7 is still quite new.