I do not have any experience with Bacula, and for a reason. The Bacula guys themselves say that Bacula is sophisticated and does not suit everybody. However, if you know that Bacula is what you want, and have decided that other solutions (like good old Rsync) are not suitable, then go ahead and dive into it — they say they have the Windows Storage daemon packaged for you in the binary installer.
Quoting from the Bacula documentation:
[...] if you are new to Unix systems or do
not have offsetting experience with a
sophisticated backup package, the
Bacula project does not recommend
using Bacula as it is much more
difficult to setup and use [...]
And in another section:
MS Windows Director and Storage daemon are available in the binary Client installer
That said, there are more free software solutions you might want to consider. Dirvish is one of them, and somebody apparently made it work on Windows, packaged it in an installer, and named it hardBackup. Haven't had any experience with that also, though, but I know that his copSSH and cwRsync work together and are great.
If you have any more questions, hit the comments. Good luck!