Why can't I install SQL Server on Windows Server 2003?

SQL Server 2000 / MSDE 2000 
 
Chances are, setup cannot continue, because you are using Windows Server 2003 Web Edition. If so, you are probably seeing this error: 
 

Windows cannot install this program because it has been disabled.    or    Windows cannot open this program because it has been disabled.

 
This version of Windows Server 2003 is meant explicitly to be a *web server*... not a database and/or application server. This is not a bug in SQL Server's setup program, this is intentional enforcement of the end user licensing agreement. (See KB #819258 for clarification.) 
 
If you want to run a true database server on Windows Server 2003, you're going to have to buy Standard or Enterprise. Or, run your web pages on 2003 Web Edition, and run the database on a different, Windows 2000 Server. 
 
That said, if your application can deal with its limitations (see Article #2343 and Article #2345), you can run the Desktop edition of SQL Server (MSDE) on Windows Server 2003 Web Edition. 
 
If you are installing MSDE 2000 on any version of Windows, please make sure you obtain a current version (SP3 or better). The same applies for any other flavor of SQL Server 2000, of course; however, be wary of applications coming from vendors who may not have considered it a top priority to update the version of MSDE that ships with their application(s). 
 
If you *are* installing SQL Server 2000 on the standard or enterprise version of Windows Server 2003, then you're probably here because, when starting the install, you saw the following dialog: 
 

SQL Server 2000 SP2 and below   SQL Server 2000 SP2 and below is not supported by this version of Windows. To run the program, click continue. For more information, click Details.

 
You can safely ignore this error message, as long as you upgrade to SP3a. Windows Server 2003 knows about Slammer and wants to make sure you are aware that you need to be responsible for getting your product up to date immediately. Hopefully, we will soon have installation CDs with SP3 slipstreamed into the product (though I recently received a 'new' SQL Server 2000 disc in my MSDN Universal shipment, and it is still RTM and not SP3). 
 
For information about this dialog, see KB #329329. You can suppress the message from appearing, if you plan to run an unattended installation; see KB #815430 for more information. 
 
You might also be having a problem because of a Windows Server 2003 Terminal Server issue. If the server you are installing on has Terminal Server installed and it is a cluster, see KB #327270. 
 
SQL Server 7.0 / MSDE 1.0, SQL Server 6.x 
 
These flavors of SQL Server are simply not supported on Windows Server 2003. The reasons are primarily security-based; when SQL Server 7.0's product lifetime ends, and Microsoft is no longer supporting it (e.g. shipping security patches), Windows Server 2003 customers would be left vulnerable to the next Slammer-like attack. So, rather than commit to supporting legacy versions of SQL Server for the foreseeable future, they decided to nip it in the bud. For more information, see KB #810391. 
 
Having said all that, it is quite possible you can get it to install (though I haven't tried it, and don't recommend it). You can try using the apcompat tool to fool setup into believing you are running Windows 2000 or NT 4.0. (I believe apcompat.exe is in the Windows Server 2003 Resource Kit, or on the Windows Server 2003 CD, or you might have to fetch a version from the Windows 2000 CD.)