Besides making your database multi-user, there could be other motivations for splitting the database. You may not want to let many people access the tables so that they can make changes to it. In a monolithic version this is possible for any user. You may also have several people developing the project in the database and there is no means of ensuring uncontrolled changes to the monolithic form of the application. One would need some kind of a source code control system to ensure that.
With splitting, the application becomes multi-user and that is a large benefit. The performance should improve significantly as main interactions are all local and on individual machines. Only the required data travels back and forth over the network. Thus time responses should improve all round. In the monolithic form the application is stored on a network shared directory on a file server. When users open a form or other elements they have to be sent over to his workstation over the network. Beyond a small size, this is inconvenient, time consuming and generates a lot of network traffic that could bog down others. Except for really simple and small databases or single user uses it makes sense to split the database.
There is database splitter wizard available with Access 2007 as well as 2003 versions. You could use that or there is a process to follow to create the split. The splitter utility may be the path to take for less experienced users. True experts will be able to optimize the application split by doing the split manually.