hiding lines in gedit

There's no way to hide source code in gedit, though there are plugins for programmers:
http://yaserxp.wordpress.com/2008/09/03/5-must-have-gedit-plugins-for-programmers/

You might want to have a look around and see if there's other plugins that do what you want (though hiding source code is not what most programmers will be wanting to do)

If your source code is spaghetti code and is getting hard to read it might indicate a deeper problem with the way you are coding. Most programmers get to the point you are at and suddenly realise the huge benefits of clear and consistent code formatting. The correct use of tabbing, blank lines, commenting the code obsessively, following the formatting conventions for a specific language, and doing all of these consistently can have great benefits for the coder and ultimately make you a more efficient programmer.

This is even more important in the Open Source programming world and when working on projects with others in general, though you will find that it makes locating problems and fixing them in your own code a lot simpler.

Find well formatted code that others have written and see how much easier it is to read and understand than badly formatted and commented code.

Chris