multiple update sites

Hi all. I would like to know about the feasability of using php/mySQL to implement a web based DB where certain parts of the DB can be updated by certain people only. There will be 300 or more people with access to update the DB each only allowed update/amend their own info in the DB. How well does mySQL handle being updated from a couple of hundred different geographic locations ? What if, say two people were trying to ammend the data in one table at the same time ? Any help greatly appreciated, Thanking you, Paul Caheny