Speed in Access 2007 Multiple Connections

I once created a donor database in Microsoft Access 2003 for a non-profit organization. On problem we had was the speed after 3 users connected to the back end. They were always connected to the back end at all times.

I've recently started using Access 2007, and I am nearly finished with a project for a 300+ employee company to manage their engineering requests. I've never launched a live project with Access 2007, and I'm wondering if this connection issue was because of Access 2003 or if my tables were set up wrong.

My question is, how many concurrent connections can access 2007 handle without it bogging down? Let's say for this purpose that there are always 12 different terminals connected to one back end on a network, will performance suffer as users try to add records? I know there will be *some* performance loss from multiple connections, but not all the users will be entering records all the time. This is how my 2003 database worked also, but for whatever reason, the 2003 project seemed to slow down for everyone regardless if all of the users were actively using the database. It seemed as if just because users were conencted was enough to slow it down.

What should I expect from Access 2007? Anything different? How should I go about setting up the back end portion?

Thank you very much for your help