I have done This Using the Samsung Galaxy 5 (GT-I5500)

1. Turn down the screen Brightness to its lowest.
2. Turn Off GPS and 3G
3. Install Android Booster (Requires Version 2.1 Upwards)
4. Close All Running Apps as this will free up the processor and ram resulting in less battery being used.
5. Turn Bluetooth and WIFI off as thease drain the battery considerably

The Guide above may only boost battery life a small amount depending on how often you use your phone and what for