The amount of credits awarded for completed Work Units for each project are awarded based on a benchmark applied to all the projects.
The benchmarks are performed on a 2.8 GHz P4 running Linux with SSE2 disabled. The machine is set to receive 110 Point Per Day. This means that a project which is worth 110 points should be completed in 24 hours when running on an identical system. And a projects which took 3 days to complete on the benchmark system will be awarded with 330 credits.
The operating system (OS) on which the client is run shouldn't be an issue anymore these days. A 2.8 Ghz P4 running Windows XP will perform almost exactly the same as if it were running Linux, because the Cores share the same source code and libraries. This used to be different, when each OS used libraries and code specific to that OS.
