In awnser to mar771 and in addition to Turbo_Ginger I'll explain my how-to. I'm not encouraging anything illegal (clearly Apple is preventing us from doing this), I want my (sometimes very expensive) software to work on my new laptop, at least untill the updates are available. Also, note that everything you do is at own risk; this is how it worked for me.
Before you start, be sure to have:
-2 machines with a firewire port (and a cable).
-installation disk (I ran the DVD, did't try with an imagefile) with Snow Leopard
-if you want to return to a previous system on the new machine a backup of the "old" system.
-a backup of the Lion system (just in case of.....)
1. Make a backup of your Lion system. (Time Machine, Carbon Copy Cloner (not familiar with) or anything else)
2. On the Lion system, use Disk Utility to make a new partition for de SL system. (in Disk Utility select de HD, enter the tab "partition" and use the "+" to create a new partition). Give it a clear name (preferably not the same name as one of your other (external) harddrives)
Keep in mind that resizing the partition afterwards is difficult, not to say impossible without loosing data on the partition. (erasing the partition is not a problem however, so you can always go back to "1.").
3. Reboot the "Lion machine" in Target mode by restarting it and pressing the "T" after the chord (when the apple appears). You can also go to "System Preferences" and choose "startup disk", there's a button for restarting in Target mode. When you see a bouncing firewire (and maybe a Thunderbolt) logo on your screen it's in target mode. While in this mode, your computer is reduced to a really expensive external HD casing.
4. Use the firewire cable to connect the two machines, and check if the lion's HDs appear as external drives on the second machine.
5. From the DVD, start the installation of SL on the second machine.
6. When you install SL, there comes a time it asks where to install SL. Choose your newly made partition ("disk") on the Lion machine. Further, follow the instructions of the installer. Even when the second machine restarts during the installation, it continues on the right partition/drive/disk.
7. Once the installer is finished, run "Software Update" to update to 10.6.8. This is still with the Lion machine in Target Disk mode! If you're unsure, you can always check Finder to see your other drives.
Note: if, for any reason, the second machine restarts and does't revert to the new partition, restart the second machine while holding the option (alt) key after the chord. This brings up a list that shows you the connected bootable drives, and with the arrows you can choose the drive to boot from. This should include the newly made SL partition on the Lion machine, which is shown as an external drive. If the new partition doesn't show it is not bootable and you have to start all over.
8. If the installation is finished and you ran software update succesfully, you can restart the lion machine (pressing the power button once to switch it off, pressing a second time makes it boot like normal). After the chord, press the option key (alt).
If all went well, you can choose now between your Lion partition and the SL partition. You now have a dual boot system with a clean install of SL on the second partition. You can use migration assistant, new installations, time machine or anything of your liking to reinstall the beloved applications.
Enjoy both systems. Glad to be of any help.