The question was fine, as I see 'installation of SQL Server 2005 Enterprise edition" as being installed with no service packs. The answer however is inaccurate (though I answered it correctly) as explained in this article

http://support.microsoft.com/kb/954835

I just encountered this last month and there are a few things. 1) No, installing SP2 or SP3 does not help this. We tried downloading the Digital versions of both from our resellers to no avail. Additionally, we tried expanding the service pack and installing via command prompt using the setup.exe hotfix=blah, solution to no avail as well. The ONLY option that would work, was forcing the server to think it only had one processor, install SQL Server and the subsequent service packs, then reboot the server into having its normal processors again.

Also per what a previous person said in this post, this server was to support a websphere application, and the requirements from the vendor were to only install sql server 2005 sp1, which it is currently running at and fine.