These are as close to a step by step guide as we have now:

http://forums.b2evolution.net/viewtopic.php?t=3297&
http://forums.b2evolution.net/viewtopic.php?t=2533&highlight=embed
http://forums.b2evolution.net/viewtopic.php?p=17029#17029

maybe someone will write a good guide for this. You can always disable the html checker, post your embed or object, then reenable it.

http://forums.b2evolution.net/viewtopic.php?p=15630#15630