hi
AFAIU from your post you have got private blocks (LAN) behind your pix firewall and you want to make them as spokes to the central hub which is basically a 1800 router.
do clarify how your spoke sites are getting connected to the hub via any routers in between or through which media ?
if you got some router in between which is in the edge and getting connected to the central hub you can always refer easy vpn server and easy vpn client setup between them.
But it all depends how the connectivity is getting established between ur spoke and hub sites.
regds