Working with CD-RW and DVD-RW

How do you Format a CD-RW in the MAC? Everytime I have tried to burn to a CD-RW with my MAC, it basically just burns a CD and it's not re-writable. Do I need to purchase an application like Roxio to do this, or is this built into the OS like WinXP.

Thanks,

You can erase a CD-RW or DVD-RW with Disk Utility. You can find it in /Applications/Utilities/Disk Utility

When your disc is in the drive, open Disk Utility, select it in the left column, and click erase. "Quick Erase" is obviously the quickest, unless you want to secure the disc by writing zeros over it.