1. Follow the appropriate steps to create a bootable USB keychain. This is recommended over trying to make a new DVD, however it should work if you rebuild the DVD Image after modifying the appropriate files.
2. Open a shell and copy the file: OSInstall.mpkg from the USB Keychain to your desktop.

   PHYS20000:~ deleteme$ cd ~/Desktop/
   PHYS20000:Desktop deleteme$ mkdir TEMP
   PHYS20000:Desktop deleteme$ cd TEMP/
   PHYS20000:TEMP deleteme$ cp /Volumes/Mac\ OS\ X\ Install\ USB\ Keychain/System/Installation/Packages/OSInstall.mpkg .

3. Create a new directory and extract the files there.

   PHYS20000:TEMP deleteme$ mkdir files
   PHYS20000:TEMP deleteme$ cd files
   PHYS20000:files deleteme$ xar -xf ../OSInstall.mpkg

4. Modify the file called Distrubition by removing the hardware checks (lines shown below).

   PHYS20000:files deleteme$ diff Distribution ../ORIG/Distribution 
   82a83,120
   > function hwbeModelCheck() {
   > 
   >     try {
   >         var modelProp = system.sysctl('hw.model');
   >     } 
   >     catch(e) {
   >         system.log('hwbeInstallCheck threw exception ' + e);
   >     }
   > 
   >     var machineCount = hwbeSupportedMachines.length;
   > 
   >     for ( var i = 0; i < machineCount; i++ ) {
   >         if ( modelProp == hwbeSupportedMachines[i] ) {
   >             return true;
   >         }
   >     }
   >     
   >     return false;
   > 
   > }
   > 
   > function hwbeInstallCheck() {
   >     if ( !hwbeModelCheck() ) {
   >         my.result.message = " ";
   >         my.result.type = 'Fatal';
   >         return false;
   >     }
   > 
   > 	return true;
   > }
   > 
   > var hwbeSupportedMachines = [
   > 	
   > 		'MacBookPro6,1',
   > 		'MacBookPro6,2',
   > ];
   > 
   >

   For your convenience, the modified OSInstall.mpkg file can be downloaded here (restricted to authenticated users).

5. Re-compress the OSInstall.mpkg file using the xar command.

   PHYS20000:files deleteme$ cd ../
   PHYS20000:TEMP deleteme$ mv OSInstall.mpkg OSInstall.mpkg.i5MBP
   PHYS20000:TEMP deleteme$ xar -cf OSInstall.mpkg FILES/*

6. Copy modified OSInstall.mpkg file to USB Keychain. If you need the old one, you can still get it from the DVD or the copy we made in step 5.

   PHYS20000:TEMP deleteme$ cp OSInstall.mpkg /Volumes/Mac\ OS\ X\ Install\ USB\ Keychain/System/Installation/Packages/OSInstall.mpkg

Now you can boot older systems than the MacBookPro with the USB keychain and will be able to install the OS . The image below shows the 10.6.3 build 10D2063a OS that came with the i5 MBP installed on our Mac Mini.

Files are Here

Distribution

OSInstall.mpkg