This how you can basically accomplish what you want - note that you'll have to use the Terminal to do this, but if you follow these instructions to the letter you should be fine.
1. Set up the Mac as you want it (install apps, etc.)
2. Reboot into single-user mode (reboot the machine and hold down the command +s keys as soon as you hear the startup sound.)
3. You'll get dumped into the terminal. Wait for the command prompt to appear and type: mount -uw /
-- This mounts the boot volume so you can edit it.
** Be very careful from this point forward.**
4. Type: cd /Users
-- Moves into the Users directory
5. Type: rm -rf *
-- Deletes all of the User folders (Shared, etc.) in the Users directory. BE VERY CAREFUL with this command - make sure you're in the Users folder. If you're not positive, type: pwd - the output should be "/Users"
6. Type: cd /var/db/netinfo
-- moves into the directory that contains the account information
7. Type: rm local.nidb
-- Clears the netinfo database and all of the existing accounts on the system
8. Type: cd ../
-- Moves up one level
9. Type: rm .AppleSetupDone
-- Remove the file that tells the OS that setup has already been run - note the period in front of the filename.
10. Type shutdown -h now
-- Shuts down the Mac
That's it! Now the system will basically be back at its "virgin" state with no existing user accounts or user files. The OS looks for the existence of ".AppleSetupDone" and if it doesn't, it reruns the entire startup sequence (movie, create user, etc.).
