As you should know by now, the EPM solution stack includes ProjectServer 2003, Project Professional 2003, SQL Server 2000 and WSS v2.0. To determine the Service Pack applied to each of them:
Project Server 2003
Check the version of the pds.dll
11.2003.0816 (No Service Pack)
11.2004.0.1707 (Service Pack 1)
11.2005.0.3801 (Service Pack 2)
11.2005.0.4110 (Service Pack 2a)
WSS V2.0 Project Template
There has been no changes since Service Pack 1. The latest service pack just reapplied what was fixed in SP1. To determine SP1 browse to \Common Files\Microsoft Shared\web server extensions\60\TEMPLATE\LAYOUTS\1033\PWAINC.
The date modified of the PWAISSUE.JS should be March 25, 2004.
Project Server 2003 Database
MSP_WEB_ADMIN table and check the values of WADMIN_VERSION_MAJOR and WADMIN_VERSION_MINOR fields.
11,0 (No Service Pack)
11,1 (Service Pack 1)
11,2 (Service Pack 2)
11,2 (Service Pack 2a)
Unable to determine between SP2 and SP2a. If you're really not sure, reapply the SP2a for the database.
Project Professional 2003
Check the version properties of the WINPROJ.exe
11.0.2003.816 (No Service Pack)
11.1.2004.1707 (Service Pack 1)
11.2.2005.1801 (Service Pack 2)
Make sure both Project Server 2003 and Project Professional 2003 are on the latest and same service pack level.
Thanks to Gord Schmidt's post on Service Packs!