1) No external .txt file. Use one of the 4 text types in mysql: TINYTEXT, TEXT, MEDIUMTEXT, or LONGTEXT. Which one you should use depends on how long you expect the advertisement descriptions would be. Take TINYTEXT if you expect descriptions with a maximum of 255 characters, take TEXT for descriptions with a maximum of 65535 characters. Take also a look at the storage requirements:
http://dev.mysql.com/doc/refman/5.0/...uirements.html
2) What do you mean with "secure" tables? Do you mean the access to your table, then google for "mysql privileges" - you will find enough to read. Or do you mean that the data in your table should be verified before inserted (and in that way it is somehow "secure")? If that's the case you should google for "mysql triggers" or take a look in the mysql manual.
van de Roobje