Update 29.04.2010: I added the latest CUs for February and April 2001. The download for the April CU doesn’t seem to be available yet, so I cannot provide any version numbers.
There are currently a lot of updates available for SharePoint (Services as well as Portal Server), like SP1, Infrastructure Rollup, SP2 and various cumulative updates. That makes it hard to keep up to date with the latest patch-level. This little table should give some overview:
| Update Name | owssvr.dll | Microsoft.SharePoint.portal.dll |
|---|---|---|
| RTM | 12.0.4518.1016 | 12.0.4518.1016 |
| October public update (2007) | 12.0.6039.5000 | 12.0.6036.5000 |
| Service Pack 1 | 12.0.6219.1000 | 12.0.6219.1000 |
| Post-Service Pack 1 rollup | 12.0.6300.5000 | 12.0.6300.5000 |
| Infrastructure Update (IU) | 12.0.6320.5000 | 12.0.6320.5000 |
| August Cumulative Update (2008) | 12.0.6327.5000 | 12.0.6327.5000 |
| October Cumulative Update (2008) | 12.0.6331.5000 | 12.0.6331.5000 |
| December Cumulative Update (2008) | 12.0.6335.5000 | 12.0.6335.5000 |
| February Cumulative Update (2009) | 12.0.6341.5000 | 12.0.6341.5002 |
| Service Pack 2 | 12.0.6421.1000 | 12.0.6420.1000 |
| April Cumulative Update (2009) | 12.0.6504.5000 | 12.0.6504.5000 |
| June Cumulative Update (2009) | 12.0.6510.5001 | 12.0.6507.5000 |
| August Cumulative Update (2009) | 12.0.6514.5000 | 12.0.6514.5002 |
| October Cumulative Update (2009) | 12.0.6520.5000 | 12.0.6520.5000 |
| February Cumulative Update (2010) (WSS, MOSS) | 12.0.6529.5000 | 12.0.6529.5000 |
| April Cumulative Update (2010) (WSS, MOSS) |
To verify the version of SharePoint you’re running go to %CommonFiles%\Microsoft Shared\Web Server Extensions\12\ISAPI and look at the file-versions of owssvrdll and/or Microsoft.SharePoint.portal.dll.
To get detailed information about hwo to deploy updates for SharePoint, check the TechNet sites on Deploy software updates for Windows SharePoint Services 3.0 and Deploy software updates for Office SharePoint Server 2007.