Clone app for imac os 10.5.8?

I want to upgrade my os from Leopard 10.5.8 to Snow Leopard 10.6. I have purchased the Snow Leopard disk.

I bought my computer in 2008. Info:

Model Identifier: iMac8,1

Mac OS X Version 10.5.8

Processor: 2.8 GHz Intel Core 2 Duo

Memory: 2 GB 800 MHz DDR2 SDRAM

Number Of Processors: 1

Total Number Of Cores: 2

L2 Cache: 6 MB

Memory: 2 GB

Bus Speed: 1.07 GHz

Boot ROM Version: IM81.00C1.B00

SMC Version (system): 1.30f1

I was told I should use a clone app to backup my os and all files to an external disk before installing Snow Leopard.

I contacted Carbon Copy Cloner, but they say they no longer offer an app for 10.5.8.

Is there another clone app that would work?

Or..... I have my original Leopard 10.5.8 cd. If there's a problem installing Snow Leopard, could I just reinstall the 10.5.8 os from the cd? And retrieve everything else from my external?

Thanks for any help!

Nina