I've written an AppleScript to change my startup disk to OS X when I'm booted in 9:
tell application "Startup Disk"Of course, change "OSXDisk" to the name of your disk containing OS X, and watch as I've broken the "set startup" line into two rows for easier display on the page -- enter it as one long row.
activate
set startup system folder alias to alias
"OSXDisk:System:Library:CoreServices:BootX"
quit
end tell
tell application "Finder"
restart
end tell
Mac OS X Hints
http://hints.macworld.com/article.php?story=20010416184548354