Actually I meant something more along the lines of this:
You have a table called users which has 5-6 columns. Id, UserId, Pass, Email, Homepage (or whatever).
Now your other table, called say myLinks has 3 columns, Id, UserId, and Links.
You will use a SELECT query to get whatever links the user already has. ("SELECT * FROM myLinks WHERE UserId = '" . $uservar . "'")
Then get the links using a while loop/mysql_fetch_array.
Then do this: "$allLinks = $row['Links'] . "," . $newLink;"
Now, wehn the user adds a link to his "my links" page you will do an insert query. Something along the lines of "INSERT INTO myLinks WHERE UserId = '" . $uservar . "' VALUES ('" . $uservar . "', '" . $allLinks . "'")".
Then when you want to display the links to the user, do a JOIN query where Users.UserId = myLinks.UserId.
You can find information about the functions mysql_fetch_array and explode() at www.php.net and you can search the sql stuff at www.mysql.com