Server Rollup Packages:
Individual Product Packages:
The Server CU is released in two different versions. The first version is in Individual Packages specific to a particular product like WSS and Project Server. These are smaller downloads but they do not include language packs or patches for other products so patches for those products would have to be downloaded and installed separately.
The second version is the Server Rollup Packages. This is a set of two rollup packages which contains all the fixes for WSS, Project Server and MOSS. These packages should be used when MOSS is part of the deployment and/or you have language packs installed. The Server Rollup Packages are much larger (~200MB each) but they will greatly simplify MOSS patch deployment.
The article below provides information on how to deploy the Project Server Cumulative Update.