Multistage.dll and Multistage2.dll functions are replaced by [ame="http://www.orbithangar.com/searchid.php?ID=4661"]Stage.dll for Orbiter 2010[/ame] add-on, so you don't need them if you install this.
As for Spacecraft.dll, I don't think many vessels still use it, and those that use it are most likely incompatible with Orbiter 2010. I don't think you will need Spacecraft.dll at all.
The most of currently available spacecraft* vessels use Spacecraft3.dll module.