Did you install the masquerading patch I posted on this mailing list
yesterday? You can also find it at the following place:
ftp://ftp.xos.nl/pub/linux/ipfwadm/patch-1.3.66-masq
It seems to work, at least in some tests I did.
-- -- Jos Vos <jos@xos.nl> -- X/OS Experts in Open Systems BV | Phone: +31 20 6938364 -- Amsterdam, The Netherlands | Fax: +31 20 6948204