A plugin (are you referring to the plugin assembly, plugin class or registration step ?) can be associated with multiple solutions within CRM - you can just open solution 2 in CRM and Add Existing (either the plugin assembly, which will bring with it the
classes, or the SDK message Processing Step)
You mention VS - are you using specific toolkits or tools that are CRM-aware ?
Microsoft CRM MVP - http://mscrmuk.blogspot.com/ http://www.excitation.co.uk