the newer one should be backward compatible with the old one ..hence, all apps that work with the old one should also work with the new one but the reverse is not true as all apps build against the new one will not work with the old one ..
..i am mostly wondering how you got yourself into that position as most people with issues are those with less than 10 posts and who didnt update the way its recommended
both libraries goes in /lib/i686 .."find /lib/i686 -name *libc*" produces:
/lib/i686/libc.so.6
/lib/i686/libc-2.10.1.so
the first being result a link to the second