The optimum time to make your bootable DVD is early in the install process. Otherwise, you won't be able to get the DMG file you need without having to download OS X Lion all over again.
This is key. The install starts automatically -- you need to stop it. At the initial screen asking if you want to press Continue, DO NOT CLICK CONTINUE!
Just leave the screen up or minimize it, and follow these instructions carefully.
Locate the Mac OS X Lion installer in your Application folder. Right-click and select Show Package Contents.
Open it by double-clicking the Contents folder.
Inside the Contents folder, find the SharedSupport folder. Double-click it to open it.
Find the “InstallESD.dmg” inside the ShareSupport folder. This is the OS X Lion installer disk image you need to burn to disc.
Righ-click it and select copy "InstallESD.dmg".
Then paste it to the Desktop.
Caution: Do not drag this file. You risk damaging the OS X Lion install application. No dragging. Pasting only.
Open the Applications folder in Finder. Double-click on the Utilities folder to open it.
Open the Disk Utility by double-clicking its icon.
Now move the ESDInstall.dmg file from your Finder desktop to Disk Utility, as shown below. Make sure you drop it right into the left-most windowpane inside of Disk Utility.
In Disk Utility, click the Burn icon.
A prompt appears, asking you to insert the destination disc for the installESD.dmg disc image burn. Insert a blank DVD into the drive. Hit Burn.
The process burns the InstallESD.dmg image to the DVD, verifies it and completes. All you have to do is wait for your new OS X Lion install disk to pop out.
If you like, use Disk Utility from the installer to perform a clean installation of Mac OS X Lion. Always proceed with caution, knowing that a clean install is just that -- it completely erases all drive contents.
Store your Lion install DVD somewhere safe. That's all there is to it!