Without having to go to Startup Disk in either OS, or using the Option key for the Boot Manager (which takes forever on my computer since I have broadband, and it searches for available network computers to boot from), I found the following hint a real time saver.
If you have multiple hard drives or multiple partitions, you can easily select which OS to use with one key at bootup without having a long delay. Whichever drive is set to the first partition (whether it be 9 or X) uses the D key (Default Partition) to boot from. In my case, I have 9 as my first partition and X as my second. If I ever need to boot into 9, I just restart and hold down the D key until I see the happy Mac. No waits, no worries, no problems.
This is helpful for older systems (like my old iMac 233A) which don't have the boot manager (Option-key) or the X key function (boot into X at startup). Likewise, you can switch your partitions so that if you only want to boot into X the odd time, set it at the first partition and hold D down whenever you want to boot into it.

