Time Machine - Restoring 10.5 with 10.4 disks

If this is a repeat, I apologize.
I've prowled the web for info on this specific problem and have not found what I need.

I'm running on an iMac and my system recently crashed. I went through the whole process of trying to reboot in Safe mode, then running Disk Utility, then 'fsck'. Looks like my drive should work, but it still freezes upon startup.

So. My last option is to reinstall OS X from my install disk. Not a big deal since I've been running Time Machine backups on an external drive.

Here's the problem: my install disk is 10.4.10 but my backups are from Leopard. I upgraded to Leopard online without purchasing a disk.

Is there any way to do a full system restore from my Time Machine backup without the 10.5 disk?

Can I reinstall 10.4, then upgrade to Leopard (or Snow Leopard), and then run my full restore? Would I then need to clone my system to a separate drive before restoring to my internal drive?

Any help is greatly appreciated. Thanks.

 

Hmmm... I thought for sure I had done a legit purchase from the apple store. Maybe not...

I think what I'll do is purchase the new Snow Leopard disks, then run a full restore from the backup on my external drive.

Any other ideas?