multisite

Hello all
I am trying to install drupal on my shared hosting plan. I have already successfully installed drupal 7.14 on my desktop windows server 2008 with IIS7. I plan to recreate the same site on the 3rd party webhost.
The hosting plan has the following:
1. Windows server 2008
2. IIS6
3. PHP 5.2.5
4. MySQL 5.0.91

I have setup my core drupal install at a subdomain http://dessites.des-us.com. It was working quite correctly, until suddenly, I get this error on browsing to the site:
Fatal error: Class 'PDO' not found in ........includes\database\database.inc on line 184

Drupal 7 / MS SQLSRV / IIS 7.5 (on localhost)

I'm trying to create a multisite setup on my localhost account with Drupal 7, and it's not been as easy as I had hoped. The biggest issue is that all of the tutorials on setting it up are for Apache and/or hosted setups.

This is what I need:

http://localhost (main install)
http://localhost/site1
http://localhost/site2
http://localhost/site3

Does anyone either know of a great tutorial or documentation on how to do this? If not, some basic steps on accomplishing this would be great. Thanks for any help.