NT Server hardware requirement

NT File Server
Component Quantity Purpose
Processor Pentium 150MHz File Server are rarely CPU bound
RAM 48MB Provides Large disk space
Disk Space 8GB 1GB for system and the rest 7GB to share in the network (~50 users)
Tape drive DAT 4GB native to back up entire server with 2:1 compression
Network adapter Fast Ethernet you want you files fast don't you; if there is a lot of traffic quite an advantage
CD-ROM Two 8X CD-ROMs file servers are often used as CD-ROM juckbox
Special hardware None Avoid unnecessary hardware such as sound cards
Special Software None Avoid unnecessary software such as anything!!!
NT Application Server

Component Quantity Purpose
Processor Dual Pentium Pro-200MHz
or a 433MHz RISC
Application server need fast CPUs for responsiveness
RAM 128MB Provides Large disk space for fast response
Disk Space 6 GB Hardware RAID 5 provides fast access and security
Backup Near-line optical disk WORM jukebox or Library drive WORM writes each database record out for permanent archive
Network adapter Fast Ethernet separate adapter for each subnetwork Bandwidth should be as fast as possible
CD-ROM One 4X CD-ROM For installation of Applications
Special hardware None Avoid unnecessary hardware such as sound cards
Special Software None but you still can install some sort of network monitoring software to track systems
NT Internet/Intranet Server

Component Quantity Purpose
Processor Pentium 100MHz File Server are almost never CPU bound
RAM 48MB Provides Large disk space
Disk Space 2GB Web site are rarely this large
Tape drive 2.0GB Sufficient to back up hard disk
Network adapter Ethernet good for internet, use Fast Ethernet for Intranet
CD-ROM One 4X CD-ROM to install software
Special hardware T-1 interface to Internet Web servers need permanent leased-line, you don't need it for LAN Intranet
Special Software Internet server software to set up the web server
NT Message Server

Component Quantity Purpose
Processor Pentium 100MHz Message servers have no real-time requirement
RAM 32MB No large caches
Disk Space 2GB Sufficient for almost any messaging server
Tape drive 2.0GB Sufficient to back up hard disk
Network adapter Ethernet Sufficient for messaging server
CD-ROM One 4X CD-ROM For installing Software
Special hardware two high speed modems For dialing into Internet or online message
Special Software messaging software such as MS Messaging or Lotus Domino MS Messaging is buggy and Lotus Domino will need a lot more then the above
NT Remote Access Server

Component Quantity Purpose
Processor Pentium 100MHz RAS server are almost never CPU bound
RAM 32MB No large caches
Disk Space 1GB more then enough
Tape drive none no use as data is only passing
Network adapter Ethernet Sufficient for messaging server
CD-ROM One 4X CD-ROM For installing Software
Special hardware 16-port serial boar with modems Inbound dial-up RAS may be as few as one or as many as 256
Special Software none Nothing special is required
NT Firewall Server

However you can use NT as a firewall I would advise you to use Linux as you can run it easily on a 80486. The security features of Linux are better (just) as well. If you still want to go for it, the hardware requirements are rather low just get a dual Ethernet. Oh, don't forget about the software. Firewall applications are not cheap.