What do you remove from a default os x install?
Is it any guides available how to reduce an HDD space occupied by Mac OS X? Languages i don't use etc.
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For languages that you no longer uses and have no plan of using again you can use the following software: Monolingual
It frees up a few gigabytes of space.
You can also see what is using up all your space by using a program called Disk Inventory X
You could also upgrade to Snow Leopard which gets rid of 10-20GB of bulk that Leopard takes up. I only recommend this if you have no customization on your system because it will break these installs.