SQL 2008 Express R2 and mutiple instances

I have a client (a small critical access hospital) and they have two applications running SQL 2005 Express and are on two separate servers. One is a Time and Attendance program and the other is a Pharmacy application. Can I consolidate onto one server and have two instances using SQL 2008 R2 Express? If I create a VM (using Hyper-V of course) and only assign the VM with a single processor will there be any issues since the physical server will have two processors? It is my understanding that Express versions will on work on a computer with a single processor and the DB cannot exceed 10 GIG in size.
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