RRAS and IPSEC across NAT

Hey so maybe you guys can point me in the right direction here. I has
RRAS setup on a windows server 2003 enterprise box with dual gig
nics. I just setup a standard NAT and am using it as a router for my
house. Everything seems to work fine except I cant get my work VPN to
go through it. It gives me an error about UDP4500 not being open. So
Im assuming this is something that has to deal with IPSEC and NAT not
playing nice. That being the case Im assuming I need to get Nat-t
going. That should by default be on windows XP so the client should
be good what am I missing on the rras box?