My dear friend,
With all due respect, you don't know what you are getting yourself into.
From your comments I can see you are not an experienced programmer. Client/Server applications are a whole different monster. There are many other considerations that will affect the success of your application.
I know why you are using MYSQL or MSAccess: Budget. That said, for Client/Server applications you need a serious database server. MSAccess is just the "Home Office" version of MSSQL. MSSQL is the real deal. Nothing wrong with MYSQL, but let's face it, #1 you want to keep technology on the same page (microsoft) and #2 MYSQL is free and open source, which raises a few security concerns.
As for data collision, I suggest you read about record locking, because that WILL BE a major concern for you, specially if you plan to use a small database system like Access. Speed will be another consideration. You will see the response speed reduce once your database grows, and by the time you want to change database servers it will be too late.
I have coded in complete accounting systems (company bought the source) that have been sold, tested, fixed, updated and improved for 5 or 6 years already, and even those have problems all the time. Consider that, these are companies that have legions of programmers working on it and they still can't get it right. Well, you know what they say, "if your program has bugs then it is useless, and if it doesn't have bugs then it is outdated."
Think about it, and find another project, honestly.
Good Luck!
