As far as I know DellEFI/NetbookInstaller has drivers (kexts) for the GMA950 only as well as all the other components of the mini 9. The 1220 has Intel X4500MHD graphics card, which has never been used in a real Mac. The nice thing about the minis is that they use the same graphics processor and chipset as Apple used in their previous-gen Macbooks/Mac Minis, which means Leopard already has proper video drivers and chipset support, which is why the Mini's can become such stable, complete Macs. With the Vostro 1220, it's obviously makes it more difficult to get OSX working, since you need 3rd party video drivers, and of course a chipset that works with your bootloader of choice. Like I said, maybe it'd be possible to get OSX working, but DellEFI is definately not set up to work with that specific hardware.
By the way, where is the 1220 only $100 more? I'm seeing $800.