If you're upgrading your server, I'd strongly encourage you to consider Linux if you can. The tools work a lot better under Linux, there's fewer configuration gotchas and performance is a lot better as well.
If you want help, Overnet Data can get involved. We would migrate it to our own Linux based platform because it makes ongoing maintenance much easier (change control, monitoring backups), and as part of the process we can upgrade Moodle too. If you still want control, we can give you access to our management systems, and we also can also integrate Moodle with SIMS which makes user, group, grouping, cohort, category and course setup much easier.