[support] Seeking Advice on Integrating drupal

I need some consultation. I've used Drupal for lightweight deployments (mostly personal blogs). But I've got a potential client who is interested in drupal for e-commerce. We're thinking through a couple of issues, and we'd like some advice:

Our client uses MSSQL for their inventory, etc. Since drupal doesn't support anything but mysql and pgsql, and since their tables would be different from drupal's regardless, we're trying to work out the best way to handle integrating drupal into their existing infrastructure. We've considered writing a script to pull data from one database and use it to update the other. We've also considered hacking the relevant modules (Ubercart) to do this on demand.

Does anyone have experience with this?