I've a stupid question. How can I shape upload using IMQ?

Instead of putting a rule in iptables in PREROUTING should i use POSTROUTING?

And another question is, can I make routing rule based on ip addresses assigned by iptables to an imq device?
The idea is, let's say i have some rules in iptables like: -t mangle -A PREROUTING -s 192.168.0.0/16 -j IMQ --todev 0

Can i route this class thru another ip, something like fwmark is doing? with iptables marking the packets and ip rule fwmark?

Best regards,

Alin