iMac 20" won't start (intel-2007)

[XCKY]

Yes I plugged in the block heater.....
Tried to reset the SMC (apple's only advice)
Tried to kick it into boot menu... no luck

managed to boot to Leopard install disk. backed into Disk Utility.... Verify System Disk produces: "Invalid B-tree node size...Disk Verify / Repair fail".

too bad too sad... no more information.

I don't know enough to know whether this is a SW failure or a drive failure, and my searches has led me here.

Also, my very first post in a forum, I read the rules and I hope I have found the right forum for this query.

Can anyone enlighten?
Thanks

[Hellhammer]

I googled the error code and it looks like your only option is to reinstall OS X. If you don't have a backup, try doing an upgrade install (doesn't erase the HD) but if you do have, erase the HD with Disk Utility and reinstall OS X and migrate from a backup