are you booting windows and OS X from the same HD via different partitions or from separate Hard Drives?

for separate HDs, check out my How-To guide.

for the same HD, we will need more info... like what your partition layout is, what partition table scheme it is in (GUID or MBR), what you want to boot ad default, etc.

it just sounds like the bootloader isn't being noticed for OS X so you can't boot unless you use the install DVDs bootloader (letting it timeout). This is an easy fix by reinstalling the bootloader (usually chameleon).

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