Getting users to view their own website running multiple sites with FTP?

Hi,

I'm using IIS 6.0 and the FTP software that comes with it. Basically, I have three websites all on one IP address (call it a.com, b.com, and c.com) that are located in C:\Websites\ as the home directory (ie: C:\Websites\a.com\, C:\Websites\b.com\, etc).

I'd like to create a user account for each website where when it logins via FTP, it's put into the directory I chose. For example: the user 'a' is put into C:\Websites\a.com\, 'b' is put into C:\Websites\b.com\ and 'c' is put into C:\Websites\com\.

I might even want two users to one domain, ie: 'a' and 'a1' are in the \a.com\ folder.

Could someone help me do this or point me to a website to explain how? I read all about isolating users and everything but am honestly lost on this part.

Thanks.