Both dws and TomK32 give useful suggestions. Usually, the number of records is not the primary concern when deciding whether or not to change from a flat-file to a RDBMS.

The limitations of a flat-file database are realized more often by having to store a great deal of information per record. Particularly if you need to store complex data like arrays or hashes.

In general, most texts describe flat-file databases as an ideal solution for implementing user authentication schemes. Primarily because they are fast and don't require complex processing. Using a RDBMS for this type of task would probably be overkill unless you are experiencing performance problems (which you shouldn't if your system is as simple as you describe).

--Jim