No, it will not lock the file and if two users run such a script at the same time, there could be issues with the users seeing a merged set of both sets of records and then deleting each other's records unless you take steps to prevent that. A field, for example, could enter the user's Account name and then your scripts could be set up to pull up in found set, process the found set and delete the found set, of just the records so "marked" with the user's account name--thus keeping each user's set of records separate from one another.
ok, can see problems - another issue - its my understanding that when a user has a record on screen that user has control of record until user moves from record - while on record others can look but can not modify fields
That's almost correct. If the user has the record open for editing, other users will be prevented from editing values in that record until the record is committed. A user can even lock them selves out of a record if they have it open for editing in one window and then try to modify the record in a different window.
This is, generally speaking, a good thing as it prevents confusion between users that can occur when two users try to modify the same record in different ways at the same time.
A record will be opened for editing if the user places the cursor in a field or clicks a control to modify the data. The data will be committed back to the database when they:
1) Click a blank area of the layout
2) change to a different record
3) change layouts
4) close the database window
5) perform a script with commit records.