As Lion has dropped Rosetta support, I was looking for a way to still run my old programs after updating to lion without having to reboot my computer using a Snow Leopard partition. Parallels can run another version of Mac OS X, however due to licensing issues, it will only allow you to run Snow Leopard Server. So you have to trick Parallels into thinking that you are installing a Server Version. To do so, you need a file called ServerVersion.plist in /System/Library/CoreServices/ of your Snow Leopard Install DVD and later on in your virtual HD. Here is how I did it. The process requires some time and you should be at least a bit familiar with your Mac, so be warned! 1. Take your snow Leopard Install DVD and create an image file from it (make sure you can write to the file) on your Hard Drive using DiscUtility (this will take some time). 2. Use TextWrangler and open the file SystemVersion.plist in the folder /System/Library/CoreServices/ on the image you just created (this folder is hidden, so you have to tell TextWrangler to show hidden files). Change the ProductName string to Mac OS X Server. Save it under the name ServerVersion.plist to the image file in the folder /System/Library/CoreServices/ . 3. Open Parallels and create a new virtual machine as SnowLeopard Server using the image file you have just modified. When the install is complete, the virtual machine will restart and then Parallels will notice again that this is not the server version and prevent you from running it. So you have to insert the ServerVersion.plist file again. Problem is, that Parallels will not let you access the .hdd file of your virtual machine. So this is where it gets complicated: 4. You have to make another virtual machine, this time with Mac OS X Lion (which is allowed by Apple). After you make this machine, add the Snow Leopard .hdd file as a second hard drive to this virtual machine. Now you have access to the hard drive of your snow leopard virtual machine and can add the ServerVersion.plist file to /System/Library/CoreServices/ as described above. 5. Start up the Snow Leopard virtual machine in Parallels and viola! 6. With software updates it gets a bit tricky again. Because of the ServerVersion.plist file your system thinks it is a Mac Server and will try to load server updates. You may choose to just ignore the updates. Or you remove the ServerVersion.plist file and perform the software update. After the install your virtual machine will not start again because of the missing file. So you will have to use your Lion virtual machine again to add the file. But once your system is updated you should be fine.