Wait for process before continuing script

Question

Hey there,
Just been working on this for a bit now in script editor. I'm still really new to the script editor functions, but would like some direction. If automater is a alternative then please help me understand how to make it work with that.
Otherwise all help is greatly appreciated!
Goal of the script:
1) load disk image. (This works)
2) open application requiring disk image. (This works)
3) Check to see in app process is running: running --> wait till it is not, when not running --> eject above disk image
Code:
tell application "Finder" -- Note when using tell Finder it gives can't get running of process
          if process "App Process" is not running then
                    set bootDisk to name of startup disk
                    set otherDisks to every disk whose (name is not bootDisk) and (name is not "iTunes") and (name is not "Applications") and (name is not "BOOTCAMP")
                    repeat with myDisk in otherDisks
                              try
  eject myDisk -- When using tell System Events it give Expected end of line but found identifier on line.
                              end try
                    end repeat
          end if
end tell
Another: Oddly the script will run the app, it throws the error while running, but the app still runs. The disk Image is also gone.
Thanks again for any helpful comments and direction.
-- Josh

Answer 1

Okay, Neil and tw^3, thanks you for your help, I got the effect I wanted cleaned up the code a smidge.
Code:
tell application "Finder"
          open document file "DiskImage" of folder "GAMES" of disk "Applications"
    delay 2 & close every window
          open application file "App" of folder "Myth2" of folder "GAMES" of disk "Applications"
end tell
delay 4.5
tell application "System Events"
          repeat
                         if not (exists process "process") then
                                        if exists "DiskName" then
                                                       do shell script "hdiutil detach \"/Volumes/DiskName\""
                  error number -128 --
            end if
                         end if
       if exists (process "process") then
       end if
       delay 10
          end repeat
end tell
Last little question about what I have, in the if statement checking if the process does not exist anymore, I put quit after the shell script to eject. but it would just hang there. Would it be better to do a repeat while? or would you just user cancel (error -128) the script from executing like I have it.
-Josh
EDIT: made it work better, used a repeat while... and moved the if not exists after the repeat...
repeat while exists "app process"
end repeat
if not (exists process "app process")
......blah blah code code
end if