Just started looking at the e-smith server, but I read the doc's to be the same as you anything other than a 0 allows access. PPTP uses port 1723 and GRE 47, so the ipchains should add a line such as:
ACCEPT tcp ------ 0.0.0.0/0 XXX.XXX.XXX.XXX * -> 1723
where XXX.XXX.XXX.XXX is your external interface(NIC)
hope this helps