I'm sorry - this is probably a hugely stupid question, but I'm a very new mac user...

I wanted to try out iblog - so I downloaded the trial, (had to do it at work and burn it on cd - I only have a dial-up connection at home) and it's file extension is .dmg.gz - so I double clicked on it, StuffIt expander opened, and then closed - nothing happened. I'm guessing I need some kind of additional software to uncompress this - but from there I'm clueless. I don't know if downloading it from another computer (a windows computer) at work made a difference.
Any ideas?
Thanks
Joanne