What is the most appropriate way to invite guests to the rehersal? Is this the job of the groom or the bride? Is it appropriate to put a note in the wedding invitations inself? Any suggestions will be appreciated! thanks.
How many people are you talking about? When I've been part of the wedding party, the bride and groom just call people on the phone.
You don't need a formal invitation to the rehearsal. A phone call will alert the members of the wedding party to the date, time, and location of the rehearsal. If you are thinking about invitations to the rehearsal dinner, those should come from the groom's parents, since they are traditionally the hosts. They might ask the bride and groom to invite people but the initial request should come from the hosts.
I assume you are talking about a rehearsal dinner or something, not the actual rehearsal itself, right? For the actual rehearsal, just make sure everyone who needs to be there knows when and where to show up, by phone, e-mail, or whatever.
For a rehearsal dinner, whoever is hosting it does the inviting (just like any other party). If that's the groom's parents, then make sure they have the list of names and addresses in plenty of time to send invitations if that is what they want to do. If it's just your two immediate families or something, they probably won't bother with written invitations; if it's a big party for dozens of out of towners, they probably will need to send invites.
If the same people (bride's or groom's parents; bride and groom; whoever) are hosting the rehearsal dinner and the wedding, I wouldn't see anything wrong with just including an extra paper in the appropriate invitations with info on the rehearsal dinner, along with any other "auxilliary" events (e.g. brunch the day after the wedding), directions, etc.