Coding...

I am pretty new with PHP, but what I've learned in the last 3 weeks is pretty good I think so far! What I'm looking to do is create a login script, and have people being able to login. Now, I have pulled scripts from sites, and everything is working okay. But the problem I have with pulling scripts from other sites, is that the mysql databases are all different. How can I import from one database into the other, so basically all the databases are merged into one main? I also know that each PHP file has to be re-done and look for the new database name, for instance if it was user_name, and the default (Main) database is username .. That I Have to rename all the php files that have user_name to simply username. If anyone is willing to help out with the project I'm working on with another programmer? Hopefully being very cost effective .. or free :) :) Thanks, Jeff