totem can be built two different ways, one using the xine backend, the other using gstreamer as a backend ( I personally cannot stand the gstreamer backend).
first, if you haven't already head over to www.mplayerhq.hu,
go to downloads and get the essential codecs package.
untar the package:
tar xvfjp essential-xxxxxxxxx
replace xxxx with the rest of the name of the package(it's usually the date).
next, make a directory called /usr/lib/win32 ( you will need to be root):
copy the codecs into /usr/lib/win32:
cp essential-xxxxxx/* /usr/lib/win32
from here, any xine based player will autodetect the codecs and use them. if you prefer xine, ( remember xine comes in two parts, one is xine-lib which is just an engine, by itself it will not play anything you need a xine front end to get the gui for it) front ends are gxine, xine_ui, kaffeine, totem (if it was built using xine instead of gstreamer) and oxine ( these are not all of them, but this will get you started).