What SQL Server Edition are you installing?
Personal Edition?
Standard Edition?
Enterprise Edition?
They have diffrent system requirements
Personal Edition: Personal Edition can works on the Windows 98, Windows NT Server 4.0 with Service Pack 5 or later, Windows NT Workstation 4.0 with Service Pack 5 or later and on the all editions of Windows 2000. This edition is related to SQL Server 7.0 Desktop Edition.
This edition has some restrictions:
maximum 2 CPU
no Distributed Partitioned Views
no Log Shipping
no Parallel DBCC
no Parallel index creation
no Failover clustering
no publishing for transaction replication
maximum 2Gb RAM
Standard Edition:Standard Edition can works on the Windows NT Server 4.0 with Service Pack 5, Windows NT Server 4.0 Enterprise Edition and on the Windows 2000 Server/Advanced Server/DataCenter.
This edition has the following restrictions:
maximum 4 CPU (up to 8 CPU on the Windows NT Enterprise Edition)
no Distributed Partitioned Views
no Log Shipping
no Parallel index creation
no Failover clustering
maximum 2Gb RAM
Enterprise Edition: Enterprise Edition can works on the Windows NT Server 4.0 with Service Pack 5, Windows NT Server 4.0 Enterprise Edition and on the Windows 2000 Server/Advanced Server/DataCenter.
This edition can use:
up to 32 CPU on the Windows 2000 DataCenter up to 8 CPU on the Windows 2000 Advanced Server and on the Windows NT Server 4.0 Enterprise Edition up to 4 CPU on the Windows NT Server 4.0 and on the Windows 2000 Server
up to 64Gb RAM on the Windows 2000 DataCenter up to 8 Gb RAM on the Windows 2000 Advanced Server up to 4 Gb RAM on the Windows 2000 Server up to 3 Gb RAM on the Windows NT Server 4.0 Enterprise Edition up to 2 Gb RAM on the Windows NT Server 4.0
Distributed Partitioned Views
Log Shipping
Parallel index creation
Failover clustering
Then there is Developer Edition,Desktop Engine,SQL Server CE