Do you have multiple yahoo accounts and want to Sign in to yahoo messenger with different accounts at a time , then here is a simple windows registry hack  which can change normal yahoo messenger in to multiple yahoo messenger
First open your run command.
type regedit


expand HKEY_CURRENT USER > SOFTWARE>YAHOO>PAGER> AND TEST
ON RIGHT SIDE
MAKE A NEW STRING IN TEST
NAME IT "PLURAL"
DOUBLE CLICK PLURAL
SET VALUE TO "0″
CLOSE REGEDIT.
Now you can run multiple instances of yahoo messenger with different accounts with out downloading yahoo multi messenger 8.0 software