I'm befuddled, what processor are we talking about ?
Interupt vector is adress where your program will jump after interupt has been trigered.
For 5'th interupt it is 5Bh. So you should write something like that:

ORG 5Bh
' do what you want in interupt
RETI

I know of no processor with a vector at 5bh

Jeff, as to the size of your ISR (interrupt Service Routine) read my post in your previous question re this.

Have fun,

Erik