I have gotten mirroring to work between a SQL instance on a Server 2008 VM and a SQL Evaluation instance on the Host Windows 7 machine with 4GB installed, but performance was frustrating at times, especialy if IE was open. If you have more than 4GB or a second machine you can install SQL on, you'll be in better shape.
For a failover cluster, you'll need at least 3 VMs, a domain controller and 2 nodes, and a tutorial on how to set up shared drives in this kind of envronment (if anyone has a favorite link for this, please post it as I'd like to do this). For 3 VMs you'll want a PC with at least 8GB of RAM , or a second PC (you can put the DC there).
Another option might be to use Wondows 2003 SP2 VMs, which can probably run satisfactorly on less RAM.