there is no problem installing this on your normal dev machine, but note that i had to manually uninstall KB949325 (in Vista it's listed under Program and Features > Installed Updates) before i could get beta 2 installed.
a good summary of changes is here: http://adoguy.com/2008/06/06/What_s_Changed_in_Silverlight_2_Beta_2.aspx
and fuller lists of breaking changes (there are lots of them!) are here: http://msdn.microsoft.com/en-us/library/cc645049(VS.95).aspx and http://blogs.msdn.com/silverlight_sdk/attachment/8574227.ashx.
the release version is expected “end of summer”, so assuming beta 2 is as solid as beta 1 was, this is the version that the classroom will first go live with--