How to supply a negative voltage from a simple battery or psu?
The best thing to do with an LM741 in most cases is to replace it with a more modern single supply opamp. 

An LM358 dual or LM324 quad is about as good, usually cheap and available.

This page
 from a project by some one at the CIT in CEBU suggests 100 PHP each which is far too dear. Digikey has them for about 20 PHP in 1's prices here and about 13 PHP each in 25's - and you get 4 amplifiers per package.

datasheet here for LM324. Single supply from as little as 3V (5V ir more is a lot better).

BUT

If you want to use an LM741 you can use a negative voltage that is greater (more negative) than -5V without affecting the results in almost all cases.

To start, obtain a 9V transistor battery or a 4 or more cell AA alkaline battery pack or other source of 5V or more.  Or a mains "plugpack" power supply of 5V or more. 

Connect the +ve terminal of the supply or battery to ground and the -ve terminal will be at -V. eg a 9V battery will give -9V etc.