LeeVal

What are you wanting to encrypt? the whole hard drive or just the home folder?. You can encrypt the home folder using FileVault. Mac can read the Windows partition and Windows can read the Mac partition providing you have installed Boot Camp, but windows cannot write to mac and mac cannot write to windows. You could create a 3rd partition to store all the documents in one place for both OS'. If your going to be writing files larger than 4GB, format the partition NTFS and install NTFS-3G driver on the mac os.

Why don't you just use a firewall service like Smoothwall, Block all ports except port 80, open maybe 443 for SSL if your going to use it. We're using a Ubuntu server with Webmin.

Will you be using a Linux server or Windows Server to host moodle? Lee