Installer says I don't have minimum requirements but I do?

I have recently copied my entire HD to an external drive and then wiped my original HD as my mac was running really slowly and want to rebuild it from scratch with only the necessary programmes etc. When I try and install CS5 Design Premium is says I don't have minimum system requirements for InDesign? I am running OS X 10.6.8 (Snow Leopard which I was previously able to install on without any problems), more details below:

Model Name:          iMac

Model Identifier:          iMac7,1

Processor Name:          Intel Core 2 Duo

Processor Speed:          2 GHz

Available hard disk space: 249GB

Number Of Processors:          1

Total Number Of Cores:          2

L2 Cache:          4 MB

Memory:          1 GB

Bus Speed:          800 MHz

Adobe stated system requirements for InDesign CS5:

Mac OS

• Mac OS X v10.5.7 or v10.6

• 1 GB of RAM (2 GB recommended)

• 2.6 GB of available hard-disk space for installation; additional free space required during installation (cannot install on a volume that uses a case-sensitive file system or on removable flash-based storage devices)

• 1024 x 768 display (1280 x 800 recommended) with 16-bit video card

• DVD-ROM drive

I have just done the exact same thing with my Mac Book Air with no problems at all.

Grateful for any suggestions/advise.

Thanks