Hi, what exactly do you mean by "log in"?
To access the mysql db on the command line, you just run the mysql command with username and password arguments:
you will be prompted for your password:
greenpeace@gppg:~$ mysql -u username -p
and you should then see the welcome message:
and then the mysql prompt (where you enter your commands):
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 44291
Server version: 5.0.95-0ubuntu1-log (Ubuntu)
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
What do you see on your system? It is very unlikely that you have caused any problems by installing the lampp packages.