MS Access is a non relational database. This means it will have issues if you have lots of people accessing it at once.
Relational databases are MS SQL Server 2008 (expensive) or MySQL (free).
You could use MS Access as a front end to a MySQL database backend. This would give you high speed relational databasing at low cost and a MS Access familar front end. Although it would probably be a bit awkward.
Alternatively you could use MSVS2008 C# to write a webpage front end.
If I was you I would hire a programmer for a month or so to put a prototype together.
Ryan