Edit: actually, it seems that Server 2003 R2 actually includes enhancements to quotas, including the ability to set quotas at the folder level in addition to old-style volume quotas. See if this meets your requirements.
You'll need to move to Windows 2008 Server to get more granular control of your quotas out of the box. Otherwise, you'll have to look into 3rd party quota solutions.
No, quotas are per volume only.
Edit: actually, it seems that Server 2003 R2 actually includes enhancements to quotas, including the ability to set quotas at the folder level in addition to old-style volume quotas. See if this meets your requirements.
You'll need to move to Windows 2008 Server to get more granular control of your quotas out of the box. Otherwise, you'll have to look into 3rd party quota solutions.