Service Pack 3 have now been release for Project 2007 and Project Server 2007 (along with the other Office 2007 products) – http://blogs.technet.com/b/office_sustained_engineering/archive/2011/10/25/office-2007-and-sharepoint-2007-service-pack-3-availability.aspx
Project 2007 SP3: http://support.microsoft.com/kb/2526091
Office Server 2007 SP3 (includes Project Server 2007): http://support.microsoft.com/kb/2526299
Windows SharePoint Services 3.0 SP3: http://support.microsoft.com/kb/2526305
As always, deploy to a Test / Dev system and fully test before deploying to any Production system.