multi DB

After reading the first half of I'm confused.

I have cpanel with host gator and each database has a prefix which is the cpanel username


after the _ i name my DB

my wpmu database is named cpanelusername_WPMU so is that what i put in to the tool at or do i just put WPMU?

thanks much

side note - i installed 5 plugins should i delete them all and then install this one first ?