default gateway per user basis

[Igor Smitran]

Alan Dekok wrote:
>   Look at the packets coming from the two gateways, and see how
> they're different.  Use those differences to write rules that match
> those differences, and return the different configurations.

Ok, let us say that we have two users: Alan and Igor

1. when Igor logs in he needs to get IP address 192.168.1.10/24 and gateway
192.168.1.100

2. when Alan logs in he needs to get IP address 192.168.2.10/24 and gateway
192.168.2.100

different IP ranges, different C classes and different gateways accordingly.
I am not sure what do i have to listen from those gateways.
Computer with pppoe server and freeradius has connection to both C classes.
I just want to route users differently. One user to more expensive link, one
user to less expensive link.
Help please?