If I read your post correctly, you wish to move a time machine backup from a disk, to the mwbe, and then use the mwbe as the time machine backup?
If so, I do not think it is possible as apparently there are differences between the network (ie apples time capsule) file structures
and locally attached disks (firewire, usb, local), however I an ready to be proven wrong!!.
My experience, using mwbe with 1..0.16 (latest available) firmware was one mac, running 10.6.2, worked pretty much straight out of the box
(had to alter one setting for tm to accept a network drive other than time capsule), the other , 10.6.2, worked for a day, then started trying to
backup everything again, ie not incrementally.
If you only have one mac, hopefully you will not experience this, if you have two, and you do get this issue, then there is a workaround.
Re your question as to where the files are, they are in /DataVolume/.timemachine (which is a hidden directory, use ls -a)
Please let us know how you get on.