configuring network alias on laptop

[Alexander Volovics]

I have a small home network and would like to connect my laptop
to the network bij adding an eth0 alias: eth0:0.

(This is necessary because I use a router and need to connect
 to my ISP with dhcp. If I use fixed IP adresses for my pc's internally
 I also have to use a fixed adress externally).

So I edit /etc/network/interfaces as follows (I only present the
relevant postion):

# The primary network interface
iface eth0 inet dhcp
name Ethernet LAN card

# The secondary network interface
iface eth0:0 inet static
name Ethernet LAN card
address 172.20.1.2
netmask 255.255.255.0
broadcast 172.20.1.255
network 172.20.1.0
gateway 192.168.1.1  
auto eth0:0

This does not work.
Now /etc/network/interfaces also contains the following:
mapping hotplug
        script grep
	map eth0

Do I also have to add a line 'map eth0:0'?
On my other (Fedora) computers '/sbin/ifup eth0' also automatically
brings up eth0:0, so why not this 'mapping hotplug'.

What are the consequences of adding anything to 'mapping hotplug'.
Does this mean you have to change some other configs?

Alexander