There is a fantastic program I use for doing dynamic scheduling called Taskline, and I think it only costs $50. Taskline is an Outlook add-in and works with several task management programs that plug-in to, or export to, Outlook as well, like Mylifeorganized, Netcentrics gtd, FranklinCovey, Mindmanager, Clearcontext , PlanPlus, OneNote and Mindjet.
Taskline automatically schedules tasks to Outlook's calendar. It schedules right around fixed appointments, and can schedule tasks directly into specific timeblocks too... the program is really amazing. When circumstances change, and the current schedule is no longer on-track, taskline reworks it all, at the push of a button... it's really cool to watch!
You can see a 5 minute video of it in action at http://www.taskline.com/default.asp
Good Luck on your quest!