I just downloaded a new game called Heroes of Newerth, however when I try to start it up it gives me a "Fatal Error" "GLSL 1.20 not available"... Is there any way to fix this or does this have something to do with my OS?

I have a Mac OS X 10.4.11
Processor: 2 GHz Intel Core 2 Duo
Memory: 1 GB 667 MHz DDr2 SDRAM

Thanks in advance for any help.