I found this page looking for the same answer. Then when I didn't find the answer here, I tried this on a hunch and it worked (SuSE 9.1).:
Of course then set the IP, netmask, etc.
I also had no use for the vlan answer as all I wanted to do was connect to my new Linksys WRT54GS wireless AP (defaults to 192.168.1.1/24) long enough to change it's IP to my local class C. ifconfig eth0:1 took all of about 5 seconds and got the job done.