Problems with Windows 7 Guest on VirtualBox 4.1.8
Oracle VirtualBox 4 introduced ICH9 chipset and 3D/DirectX graphical support for guest operating systems, but the new features are "not quite there."
I created a Windows 7 virtual machine using the ICH9 chipset instead of PIIX3, but ran into a lag/freeze/hang problem where Windows would just freeze randomly. The freeze would last for 5-6 minutes, then Windows would pick up from where I left off as if nothing happened. I tried the registry fix described here but it did not work for me.
For the DirectX support, I followed all of the instructions for installing the WDDM drivers in a Windows 7 virtual machine via the Guest Additions. I tested several simple applications that use DirectX, including iTunes 10 and Roxio Creator Pro 2012. iTunes store's home page loaded, but clicking on any link would not display any other page. Cover flow worked, albeit slowly. Roxio would not start at all, although certain of its subprograms worked ok.
After disabling the DirectX 3D support drivers by uninstalling and reinstalling the Guest Additions, Roxio will start but certain programs will not run. Also, iTunes store now works properly, but cover flow is disabled as it relies on Direct3D.
The observations above are not intended to denigrate the amazing work of the VirtualBox developers. The graphics functionality has specifically been labeled experimental. I was simply testing the limits of the functionality of the latest release. My Linux server specs: Intel Core i7 920 processor with 24 GB RAM, two Hitachi 1TB RAID 1 hard drives, Sapphire Radeon 4650HD graphics card, AMD ATI 11.6 drivers, Fedora 14 (18.104.22.168-106 64-bit kernel), and VirtualBox 4.1.8.
Update: VirtualBox 4.1.10 may have solved some of the problems, but I have not tested them as of yet.