user logins – showing graphs etc.

Hi There,

I am now getting into wordpress and love it – but have a question that might save me some time.

I am just wondering what the best method is for achieving the following

* displaying a user login dialog/signup
* access the user id from within php (i.e. if I write my own plugins)

Basically what I am doing, is allowing users to measure and plot their progress over time (e.g., weight), and using jQuery to generate the graphs etc. I can do this as a separate webpage, but would like to integrate it into wordpress.

The only thing I would like to know is the typical method for creating user accounts, and accessing the user login id within php – and the best method for integrating such php (i.e. do I need to write a “plugin”).

Any tips/suggestions would be greatly appreciated!