I am writing a bootloader program for ARM cortex-M3. for this i need to use the embedded assember of the keil. i am unable to configure the assember. kindly suggest.
Do you - really??
please see this thread: http://www.keil.com/forum/17856/ and be sure to read the linked article.
Note that ST have bootloader examples for their Cortex-M3 that manage perfectly well without assembler!
"i am unable to configure the assember"
Rather suggests that you are not ready to be doing this!