Hi Vinod,
Exactly.. That's the place I am searching where I could write the code for parties involved because I need to do it generic for all Business Transaction.
if that transaction has the mainteined that particular partner function i need to check that and maintain the partner function...
For example : I have maintained Business Partner ( Lawyer ) in opportunity , So if i create opportunity for lawyer(Account) the Involved parties by default should be poppulated with lawyer. So can u please guide us for that 
thanks agani..
And thanks a lot for the pointer...