Select IP Alias by user/program?

Hello.

My system:
Debian testing (kernel: 2.4.20-3)
2 network card, other to home network and other to adsl box.
I can lease 5 different ip address from my service provider dhcp server.
Firewall is shorewall (http://www.shorewall.net/)

Any idea how I can reserve 3 different ip address from service provider to
my firewall machine? (ip aliasing?)
How I can after that select what interface program use? (example: irssi,
lynx, etc)
And how I select interface by user basic? (Example: root use eth0, test use
eth0:1 and Santa use eth0:2)

Regards: Tommi
Ps. Sorry my poor English