Hi St,
A "bare minimum" figure is really pointless, as the system will rapidly
become unusable. As with other versions of Windows, that actual drive
space occupied by the OS is *not* the minimum space needed since
additional space is needed for expansion of temp files during
installation and operation, as well as for paging. How much is not
defined by a set amount, but rather by how the system is used and what
programs are installed to support that use.
Vista Business recommends a minimum of 40GB drive space with at least
15GB free space. The actual amount occupied by the system files after
installation will vary dependent on which features are installed,
generally between 5-7GB.