Virtualization is an instruction set on the CPU, not the graphics card. The Q8200 does not include it, but the Q8300 and Q8400 do. Upgrade to one of these (or go even higher, to the Q9000 series) provided it doesn't void your warranty. In my experience, Dell doesn't really care how you modify the system, but if there is a problem, it must have all of the factory provided hardware installed before being serviced.
Is there a particular reason why you need the Virtualization instruction set anyway? If you're not interested in running Windows XP Mode once under 7, or another virtualization product like VMware, then I wouldn't worry about this.
I can't imagine why Aero wouldn't be supported on that Radeon 3450. It's at the lower end of the scale, but should still be able to run Aero.