routing problem

[Donatas]

please see the scheme below:


user1---[usa]-------->machine1                              machine2
                                  vlan1(default gw)                   vlan1---------------->em0(USA)      ?<---------------
                                                             -=-=-=-=-->        (zebra,ospf)                                           
user2==[europe]===>vlan2(ospf,zebra)                   vlan2==========>em1(EUROPE)   ?<==========


I've encountered a serious problem. I must differentiate USA and EUROPE subnets into two different vlans between two different machies. First machine gets USA traffic to em0 and EUROPE traffic to em1. When user1 tries to reach USA IP, he does not gets any routes via ospf, so he passes through machine's1default gw via vlan1. When user2 tries to reach EUROPE IP he get's ospf routes from vlan2 and goes out via that vlan2. The problem is with inbound traffic. How can machine2 divert inbound USA traffic to vlan1, and inbound EUROPE traffic to vlan2?The problem should be solved in IP level only. Zebra(ospf) is unable to do that and I cannot change vlan or interface structure because of certain reasons:(
Thanks for any ideas.

bsd5.4