If this is the Sage medware software then the site indicates Windows only. I don't know of any "free" native opensource medical management software.Try -->
here. And check this article -->
here.It's possible that some other web based apps may work with FireFox on Linux. There are business management AIO "stacks" that you may be able to adapt. You could also look into Alfresco document management but I don't think it's an AIO. You may have to generate invoices,charts, etc separately with specific software and then track them with Alfresco.
Wish we could be of more help but these kind of applications have a tendency to be very Windows specific and because MicroSoft and friends want to be your partner for life (whether you want or not), they encrypt these formats so you can't leave. Probably will have to ask yourself why you are leaving Vista. Is Win7 an option? Migrated my business to Linux 5 years ago and haven't looked back but the kind of software you're looking for may be hard to replace in the foreseeable future.