How to refer to a message window in Mail.

Question

How do I refer to a message that is in the frontmost window in Apple Mail? I have a Filemaker script that saves a report as PDF and attaches it to a new email message in a new window. Now I want to use Applescript to enter email addresses in the To: and CC: fields in the new email message containing the attachment.
All the examples I find refer to making a "new outgoing message" such as this:
tell application "Mail"
set newMessage to make new outgoing message with properties {subject:theSubject, content:theMessage}
tell newMessage
set sender to theSender
make new to recipient at end of to recipients with properties {address:theRecipient}
end tell
end tell
This won't work since I already have a new message. All I want to do is enter new recipients. But it seems I need to refer to this message as something more than "the front window".
Any ideas?
  Mac OS X (10.4.7)  
  Mac OS X (10.4.7)  

Answer 1

01. In 'FileMaker Pro Advanced' the following fields, in the order shown, were created:
Sender: (field 1)
To:
cc:
Subject:
Message: (field 5)
-- The code below works with the above fields.
set tFlag to 0
set tLIst to {}
tell application "FileMaker Pro Advanced"
activate
set tFields to (fields of (current record of database 1))
set {tSender, tRecipient1, tRecipient2, tSubject, tMessage} to {(item 1 of tFields), (item 2 of tFields), (item 3 of tFields), (item 4 of tFields), (item 5 of tFields)}
-- 'Command 1' is my 'New Script', wiich calls 'Send Mail'.
tell application "System Events" to tell process "FileMaker Pro Advanced" to keystroke "1" using command down
end tell
tell application "Mail"
activate
set eAddresses to (email addresses of accounts)
repeat with i in eAddresses
copy (item 1 of i) to end of tLIst
if ((item 1 of i) is equal to tSender) then set tFlag to 1
end repeat
if (tFlag = 1) then
repeat until ((name of window 1) is "New Message")
end repeat
delay 1
tell application "System Events" to tell process "Mail"
-- Exercise for the student
end tell
set nMessage to (outgoing message 1) -- Targets the front most 'Mail' window for the following actions.
tell nMessage
set visible to true
make new to recipient at end of to recipients with properties {address:tRecipient1}
make new cc recipient at end of cc recipients with properties {address:tRecipient2}
set subject to tSubject
set content to tMessage
-- send -- Un-comment when the above code is completed.
end tell
end if
end tell
Use 'tList' in the 'tell application "System Events" to tell process "Mail"' ... 'end tell' block of code to properly set the e-Mail window's 'Account:' pop up menu, to the desired 'sender'.
  Mac OS X (10.4.4)