VM software for personal use?

[Richard Lawrence <richard.lawrence@berkeley.edu>]

Hi all,

I am looking to run some virtual machines for personal use: I'd like
to (attempt to) try out some alternative OSes from within my Lenny
host.  My goals are to be able to get a taste of some more "exotic"
systems (maybe: BSD, Plan 9, Open Genera) without threatening my
stable environment, and with easy cleanup.  My understanding is that
the easiest way to do this is to run these systems as virtual
machines, though if others have different suggestions, please let me
know.  

I would also just like to learn more about running a VM, since I'd
like to be able to help my dad out. He has a Windows development
machine that is choking to death on anti-virus software.  It would be
nice to be able to help him convert that into a VM inside GNU/Linux,
so the machine will become usable again for things other that don't
require Windows.

I am wondering if others have recommendations for where to start with
this project.  I am pretty much a complete newb with respect to
virtual machine technology; I don't really know how to assess whether
Xen, VirtualBox, QEMU, KVM, or something else would be the best
software for me to start learning.

I value:
- free over non-free
- ease of use and good documentation over performance
- installation via apt and reasonable default configuration
- simple networking on commodity hardware
- other basic integration with host OS services (perhaps file sharing,
USB, printing)

I realize that these things may not all come in the same package. But
if they do, or if someone could give me some guidance about how to
sort out the tradeoffs, I'd be most appreciative!

Thanks,

Richard

P.S.  Apologies if this question seems too far off-topic for
debian-user.  If there's a better place to ask this question, I'd like
to know that, too.