Added some comments in Allen's code and inserted the path and filename to match your setup. The username can be used as a macro in kix. It has the @USERID macro that holds the current username. I also placed it outside quotes so it gets interpreted as it should.

I tried it on a test file and it works fine.

 Code:
Break on

;Set the filename and path of the file to be checked.
$filename = "C:\Documents and settings\" + @USERID + "\Application Data\Microsoft\Outlook\data.txt"

;Set the maximum size if the file (in bytes).
$maxsize = 5000

;Check if the file exists
If Exist($filename)
	;File exists so get the file size and see if it is bigger then the max file size.
	If GetFileSize($filename) > $maxsize
		;File is bigger then the max file size so delete it.
		Del $filename
	EndIf
EndIf 

;Sleep for 5 seconds so you can read the screen output if there is any.
Sleep 5
_________________________
Mart

- Chuck Norris once sold ebay to ebay on ebay.