MS'SQL Server 2000 is mainly for small-middle corporation,while oracle's oracle 9i is for large company.
MSSQL is mainly for Windows 2000,although it may have enterprise edition for windows 2k advanced server.
Oracle 9i is mainly for Unix.like AIX,HP UNIX,SUN Solaris etc. Although Oracle has it winnt edition product.
You can get more information from the web site www.tpc.org