I assume the ADC08 is an 8 bit A/D.
So you will need to firstly convert the 8 bits into two 4 bit BCD words. I posted ideas on this topic some time ago, do a search of my posts.
Then you will have to convert the BCD into the 7 segment format. This can be done by drawing Karnaugh maps, one for each segment.
I don't know why you want to multiplex.
There are several reasons for multiplexing, here are some examples.
If you want a PIC to drive say 4 displays, multiplexing is necessary since the PIC does not have enough i/o lines to dirve them directly.
If you need to minimise the wiring, eg. the displays may be remote from the main PC board.
Computer keyboards use multiplexing in order to minimise the hardware and wiring.
Len