Database access directly from Windows client - good or bad?
Assuming it's a multiplayer system
I don't know if this is inherently good or bad. If there is no business reason to centralize data access, not connecting directly to the client application's database in the database is not a problem. You will want to create a decent level of data access whether it was done on the client or through a centralized data access server.
You mentioned multi-user mode, depending on data and usage, there may be transactional issues that can be an argument to centralize events with, but they can be handled from multiple clients as well.
Quite a common requirement for business applications, so GOOD.
Don't try to use MS Access as a background for a multi-user application. That would be bad.
For security reasons, I prefer to access the database through a web service. This way you don't need to have the database id / password in the client application.
I would recommend using stored procedures as inline coding of the database is insecure (e.g. SQL injection) and if there are changes that need to be made to the stored procedure in the future, this is a good opportunity that you don't have to deploy the updated application (depends on how it is encoded).
If you are worried about some types of race conditions between users, you can use Commit / Rollback transactions.