So, to make this clear before I go and brick my Mac:
1. Make 2 partitions
2. Erase my main HD with ML installed
3. Reboot and go on to the empty hard drive
4. Reinstall Lion over the Internet
If this is correct, then I only have one problem: my computer will not connect to my wifi when in recovery or on the boot screen
No no no. I apparently didn't explain well enough. Here are more in depth instructions. Just make sure you have backed up your machine so you don't lose everything, as the downgrade process involves erasing your main HD.
Take an external hard drive that can be completely wiped, and make 2 partitions on it. Name one Mountain lion, and one Lion.
Go through the steps to make the ML partition on your hard drive a bootable disk based on the latest beta. If you don't know how to do that from disk utility, here is how you do it:
http://www.macworld.com/article/1161069/make_a_bootable_lion_installer.html
Make SURE you make a Mountain Lion install for the ML partition though.
Then go into the app store and re-download lion. Right click on it when it is done being downloaded, and press show package contents. Now go to Contents>Shared Support>Install ESD and make your Lion partition on your hard drive a bootable disk from that.
Now, Restart your machine with your hard drive with your 2 partitions plugged in, and hold down option as you restart. Choose the Mountain Lion partition from your hard drive. Once it boots, go to disk utility, and click on the mac's internal hard drive on the left. Now, click the partition tab and click where it says current, and make it say 1. This will completely erase your mac's hard drive, so make sure you have a reliable backup. Click apply, and then what I usually do just to make sure everything is completely gone is go to the erase tab and erase the disk a second time.
Now, quit disk utility and shut down. Boot up holding the option key, and this time select the lion partition from your hard drive. If you can't boot this still, and are getting that symbol you got above, you didn't do something right here. If all went well, you should be prompted to install lion.