asterisk users - May 2005 - find free e1 channel

hi list,

how can i organize several pcs installed with asterisk and e1 cards to be 
seen from an asterisk server as one? so if there is a voip call that needs 
to be forwarded towards the pstn the asterisk server should find a pc that 
has free channel on it's e1 cards that is connected to the pstn side.

                 /-- Pc1 - E1-\
VOIP -> Asterisk--- Pc2 - E1--PBX->PSTN
                 \-- Pc3 - E1-/

i can not put all e1 cards into one pc since the codec translation that is 
pretty cpu critical.

thank you,

bdz