Will gingerbread system apk apps upgrade over froyo's? On my froyo , I just found several apk files of gallery, FMradio, etc etc inside "/" directory using filemanager.. I was wondering if gingerbread's system apps can be used to "upgrade" over these froyo system apps.. Would it void my warranty? would it cease OTA upgrades?

If anyone could also give the sources to gingerbread system files apk's it would be good.
It would almost certainly void your warranty, even if you somehow managed to do it without rooting.  They also probably wouldn't work -- 2.3 introduced several features that aren't present in 2.2.  And apart from Google apps, many apps like Gallery/etc. are device specific.