1.7 patch problems? help!

i can't seem to figure out how to upgrade no limits 1.7 on my mac PPC g4,
my os is 10.5, i just can't fgure out what to do with '~.dmg.gz' ... i open that file and then have another kind of file i'm not too familiar with. i must admit i'm not the most computer literate person i know, but i do rely on the automatic ease of mostg mac operations.

can anyone please explain what i need to do, or where i'm going wrong?
thanks

I believe a .dmg usually opens up into a disk image which you should then be able to open and find the file inside.