Using database is preferable in this situation IMHO, because:
- it is more scalable (if more users/more fieds added, flat-file performance will degrade much faster
- will add SQL/database skills to your toolset. It is better to start learning it on this kind of simple projects, so next time, when needed, you'll be ready...

I agree with dws that reading small flat file with file caching can be faster, but I believe we need to ask business questions: if small number of users, speed gain will not be important enough for not applying scalable solution, so why not to do it properly? Next time, when cynix will need accomodate more users, s/he can start with something better than flat files...

Just my $0.02

pmas
To make errors is human. But to make million errors per second, you need a computer.