I will answer your question about splitting. Basically, if you are going to share the DB, you MUST split it in order to avoid major problems.
Look at post #8 in this thread:
i guys, I've got a very specific split database/network problem. I have created a front end/back end solution and when I install the back end onto the company C: drive and the front end anywhere else (eg. other partitions on the server with a different drive letter) everything is fine and...
www.access-programmers.co.uk
Now, I will answer your question about WHERE to put a shared BackEnd file.
IF the file is going to used via something like SQL Server or MySQL or ORACLE or Informix or Sybase - all of them being ACTIVE database servers - then you do best putting the DB on its own machine that will act like a server. It will run its SQL engine locally and you talk to it through some variant of ODBC protocols.
IF the file in question is a "native" BackEnd of Access, one that was created by using the file splitter, then that database file is PASSIVE. It can sit on any machine that supports Windows File Sharing. Technically, it doesn't even have to be a server-class machine because all it will do is file services. The work on a native Access BE file is done by the FrontEnd machine, which is running Access and merely using Windows File Sharing protocol to get or put data from PARTS of the BE file. Technically, the protocol in question is called SMB or Server Message Block. (And some vendors include something called SAMBA as their proprietary name for a version of that protocol.) As long as the BE file's host is set up for sharing, you are good to go and do not need to worry about anything else.
IF you have a small shop, you might not have a formal domain, but as long as you have connections via some sort of intranet, you are probably going to be OK. If you have an actual domain controller in your network, you will be fine because that will make addressing easier. You might wish to look up UNC mapping, which takes the form of
\\computer\share-name\folder\folder....\folder\database-file (and I made that kind of a deep path but it doesn't really have to be very deep at all.) Drive-letter mapping works in a small shop but you should be very careful about how you do that because of accidental drive-letter conflicts. UNC mapping is unequivocal and usually quite efficient.