Surely the iMac's still covered by Apple Care if its the 24" model, you could get it fixed for free by Apple.
Failing that, you could try this:
1. Start up your iMac in target disk mode (hold down the T button during power up).
2. Connect the iMac and your MacBook Pro with a firewire cable.
3. Boot your MBP from the MBP install disks (not the iMac ones, well try the iMac ones first but it will probably say incorrect system or something).
4. Then install OS X onto the detected firewire drive (which is the iMac drive).
5. Restart the MBP and hold down the Alt key to choose to boot from the Firewire device and then once loaded, do a system update to get all the updates.
6. Shut the MBP off, shut the iMac off, remove the cable and start the iMac up.
While on pre Intel Macs it was usually possible to install from any Tiger disk, the new Intel Macs have specific versions of Tiger. I think a reinstall disk will only work on the machine its designed for but then if OS X is later updated to the newest version that supports both machines then it could work. I haven't tried this mind you, I've done a similar method without having to do the software update on some G3 and G4 macs though.
