I wouldn't even imagine of recomending that you use MySQL. While it seems like you're in zero danger of hitting MySQL's ceiling, there's a lot of us that have found it worthwhile to not even bother and have been using the featureful PostgreSQL instead. It probably won't matter to you for at least another year, however.

Each of the databases MySQL and PostgreSQL can contain multiple tables and are normally expected to. So you could have a list of users, a list of currently authenticated sessions, a list of data on your web sites, etc. When you said "database" you really meant "table." You can have lots of tables in each database. Of course, to interact with a database you'll need to have learned some of the SQL language. Since you're doing this over a CGI web connection, you'll also need to learn about CGI. All in all, you're learning at least three languages simultaneously here. I once found the book Learning Perl by Randal Schwartz to be very helpful along with CGI Programming with Perl. Both are available from http://www.oreilly.com for not a lot of dollars.

1. Use the Perl Data Base Interface (DBI) module
   This is a Perl module that lets you write database code in standard SQL regardlesss of the actual database you are using, including flat-files. You'll pretend you're using an actual rdbms, write your code in sql, and DBI will take care of translating that into the commands that will interface with your flat-file. A good introduction to the Perl DBI is http://www.perl.com/pub/a/1999/10/DBI.html. Then, if you decide later on to switch to a real db, you'll have just a few lines of your code to change as you tell DBI which type of db to interface with, instead of the whole thing to re-write. All this work on DBI's part does come at a price - it adds a layer of interpretation and slows things down a bit. But you won't notice it witha flat-file until your user list approaches 1,000 or so rows.

2. Raw Perl. Here you go:

username|password|fname|lname|user_info
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<form action="myscript.pl">
<select name="user">
<OPTION VALUE="uname_1">user name 1
<OPTION VALUE="uname_2">user name 2
</select>
</form>
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# use the CGI module, this automates processing of form input and take
+s care of a lot of security issues too
use CGI;
my $query = new CGI;
$user_to_delete = $query->param('user');

#load the user file into an array
open(FILE, '<user_data_file.txt');
@user_data = <FILE>;
close(FILE);

#to find the row with your user, cycle through the rows, parsing each 
+one and looking for the user name, and write all lines back to the us
+er database except the one for the user in question
open(FILE, '>user_data_file.txt');
for $i (0 .. $#user_data) {
     @this_user_info = split(/\|/, $user_data[$i]);
     if ($this_user_info[0] eq $user_to_delete) {
          #do nothing
     }
     else {
          print FILE "$user_data[$i]\n";
     }
}
close(FILE);
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