Correct you can place many SQL databases within a single SQL Server instance. With SQL 2005 you can have more than one schema within each database.
I'm assuming that you will be putting Windows 2000 Standard Edition on the server. With Windows 2000 standard there is pretty much no reason to use SQL 2005 Enterprise.
Keep in mind that your licensing costs will go up as you add more CPUs to the server. For standard edition your licensing costs come in at $5,999 per processor for the SQL Server. If you have a quad chip server that's $23,996 for the SQL Server.
If cost is going to be a issue you may want to look at the lower end versions of SQL Server 2005. Workgroup edition is more scalled down version that Standard edition, but it only costs $3,899 per CPU. There is also the Express edition of SQL 2005 which is very scalled down, but it also free to use.
Use the link that SQLDenis posted and figure out which features you really need before deciding on the version of the software that you are going to use. Keep in mind that the Express edition doesn't come with the same user interface that the other editions come with.
Denny
MCSA (2003) / MCDBA (SQL 2000)
--Anything is possible. All it takes is a little research. (Me)