This topic is already discussed in an FAQ here (please look through the FAQs before publishing questions to the Forum):http://iwebfaq.org/site/iWeb_Multiple_websites.html
Have a look at Chapter 1 and the rest of it.
iWeb is a software made by Apple Inc. to easily build websites.
There's also a canadian web services provider called iweb but the two things are not related to each other in any way.
In addition to iWeb you also need a hosting. iWeb only builds doesn't host.
Build your website with iWeb. Then Publish to MobileMe (Apple) (I wouldn't recommend it for multiple websites) or to a folder upload it to any host you'd like to use (recommended if publishing multiple sites) the same way you did for your other website.http://iwebfaq.org/site/iWeb_Folder_FTP.html