You've got me confused!
Microsoft Vista is an operating system for a PC (in the same way that XP is). It has nothing to do with providing e-mail addresses. These are either provided by your ISP or by another e-mail provider, such as GMail or Gawab. It's these people that determine how many addresses you can have.
You can have as many e-mail addresses as you like (irrespective of your operating system) with Gawab. These can either be used with an e-mail client, such as Outlook Express, or via a web-based interface. The service is totally free:
http://www.gawab.com/webfront/main.php
(See 'Features>POP/SMTP' for details of how to set up an e-mail client, e.g. Outlook Express. Then click 'More countries and cities' to choose a domain name. I usually use 'alex4all.com' or 'gawab.com').
Chris