The server installs in less than 700Mb (IIRC).
http://wiki.contribs.org/SME_Server:Documentation:Administration_Manual:Chapter4
Category / Minimum Specifications
Architecture = PCI-based i586 or i686 compatible processor
Processor speed = 400 MHz
RAM = 256 MB
Hard Drive = IDE or SCSI - at least 4 GB
SCSI adapter = SCSI adapter must appear on the supported list (only necessary for SCSI systems)
Ethernet adapter(s) = The ethernet adapters installed on your server must appear on the supported list.
Modem (for dialup only) = Only modems that are Linux-compatible may be used.
WinModems are not supported.
CD-ROM drive = ATAPI or SCSI
Monitor = any
Graphics card = any
Category / Recommended Specifications
Architecture = PCI-based i686 compatible processor
Processor speed = 1.5GHz
RAM = 512 MB
Hard Drive = One or more IDE or SCSI - at least 40 GB
SCSI adapter = SCSI adapter must appear on the supported list (only necessary for SCSI systems)
Ethernet adapter(s) = The ethernet adapters installed on your server must appear on the supported list.
Modem (for dialup only) = Only modems that are Linux-compatible may be used.
WinModems are not supported.
CD-ROM drive = ATAPI or SCSI
Monitor = any
Graphics card = any
It offers the following services out of the box : FTP, Web, email, PPTP VPN, antivirus and antispam filtering.