My laptop had Mac OSX, Win7 and BT4 triple booting.

Today, I tried wiping out my BT4 partitions, but could not find Gparted on the BT5 DVD. I used a BT4 DVD to boot up and wipe out my BT4 partition on my laptop. I then booted up the BT5 DVD and started the installation to the 40GB of "Free continous space" on my laptop I created earlier. Near the end of the installation process, I click the "advanced" tab to change my boot loader location, but for some reason it will not let me pick the Linux partitions to write the boot loader to (the "OK" button is grayed out." If I pick my OSX or Win 7 partition, then the "OK" button is enabled. I know if I write the boot loader to either of these two partitions, I'm probably going to mess up my laptop. I never had this issue with BT4. Any advise would be appreciated.