I have had the crash issues you describe with IE7, although it has gotten better since its initial release.
OK I should say that IE does crash or lock up occasionally as well for me however FireFox does it at twice the rate IMO. I really want FireFox to succeed but IMO most of the oohing and awwing over it is not founded in reality, it allows malware through just the same as IE, it’s buggy or buggier than IE, the few websites I use show worse rendering in FF. I use FF the most because I can do more with it with plug ins than I can with IE and that is the only reason why it stays as my primary browser.