it seems youtube stopped to store whole files in the browsers cache, the cache places in windows xp:
C:\Documents and Settings\zak\Local Settings\Temporary Internet Files\
C:\Documents and Settings\zak\Local Settings\Application Data\Google\Chrome\User Data\Default\Cache
C:\Documents and Settings\zak\Local Settings\Application Data\Opera\Opera\cache

as an example a video 4.6 MB are partitioned to 1.69, 1.69, 1.2 MB in the caches of ie, chrome, opera. i test this today for the 3 browsers.
so the procedure used in this previous thread will not work, indeed i was utilizing the old way every day instead of using special utilities so google seems wants to make things harder for the people to rip the videos from the cache and to benefit more the commercial software makers.