I am aware of hard drive encryption options like TrueCrypt and other tailor-made solutions, but I am curious as to whether Windows security provides any kind of protection for a drive that is removed or stolen from a PC. If I grant read-access to a directory only to members of one group, can any user access that directory after the drive is moved to another PC? What about accessing the drive from a Mac or Linux box?
Permissions alone can't protect a stolen drive. Linux and Mac won't honor NTFS permissions and you will be able to do what you want (provided you have the ntfs-3g driver). However, if you use NTFS encryption or the new Bitlocker (Vista Ultimate+), you'll be better off.
Windows Encrypted File System (look at the efs tag here) will lock away your data quite good.
Permissions and related access control will only prevent users defined by the windows 'administrator' from accessing across their ownerships (that too within the limits of system stability and vulnerability).
Both TrueCrypt and EFS will protect your data within the limits of the encryption technology similarly. It would need someone to know your password (by whatever means) to reach your data.
But, having said that, I would prefer using TrueCrypt over EFS.