Q: HI I have installed snow leopard and updated but wont allow me to install mavericks can you help? Please!

In Applications/Utilities/  start SystemInformation. What Model Name and Model Identifier?

Your said Intel Duo: this iMac has max 10.6.8,

But with the ModelName and ModelIdentifier, I can tell you what the max OSX is for that model.

Mavericks compatibility:

OS X Mavericks: System Requirements

Your iMac is introduced in Sept. 2006

The highest you can go is Mac OSX 10.7.5 (Lion)

ckuan is correct. Lion max.

You have only 2GB of ram memory, that is low to use large apps with large files.

But your iMac can only address 3GB of ram, even when you put in more.

200-pin PC2-5300 (667MHz) DDR2 SO-DIMM

Although it is 50% more, it still is low.

Lion can purchased in the US here: http://store.apple.com/us/product/D6106Z/A/os-x-lion

The maximum amount of RAM for your Mac is 3 Gigs.

http://www.apple.com/support/lion/

No, you can't get Lion if you don't have Snow Leopard because the AppStore App is in Snow Leopard.

See: http://www.apple.com/support/lion/installrecovery/

Check to make sure your applications are compatible. PowerPC applications are no longer supported after 10.6.      

Application Compatibility

Applications Compatibility (2)