MSSql or SQL Server Wrapper for custom module? I'm writing a custom module and I need to access data that is currently stored in an MSSql database. It would be great if I could use the built-in database abstraction layer, but obviously that isn't possible.

Are there any modules or resources that provide a similar abstraction layer for MSSql?

If not, how would I go about writing my own? I feel very badly about just putting the connection and query strings directly in the module, it seems so.. antiquated.
Since you didn't specify a Drupal version, I'll try to answer for both Drupal 6 and 7.

Drupal 7

See http://drupal.org/project/sqlsrv

Drupal 6

Even if there would be SQL Server integration in the official db-api, it wouldn't help you much because with Drupal 6, you can only connect to multiple databases of the same type. This is why https://github.com/dereine/views_pgsql was created for example.

However, it might be an option to use the DBTNG project, which is a backport of the new Drupal 7 database abstraction layer and use that in combination with the sqlsrv project. I haven't tested that but it could work. And if not, maybe with a few changes (which you could contribute back)