Found this from overgrow.com - cached version on google. You can use fags but you have to boil the water before using.

Contributed by: Funky Smile
Submitted: February 8th, 2005

Get 2-3 Marlboro red ciggies, empty them out in 200ml of water and leave to stand overnight (or 24hrs).

After that the liquid will be brown/black, *boil it for two or three minutes (no more) to kill any possible pathogens and cool it down, even better would be to leave it in the fridge to get really cold (but don’t freeze it).

Once that’s done spray 2-3 times a week. A few drops of liquid detergent or insecticidal soap help to lower the surface tension of the water, making spraying more effective, as instead of droplets, the water forms a film over the plants and bugs.

Wear gloves whenever handling the solution, and a mask whenever spraying it. A Nicotine solution can poison the grower too!

Vegging plants can be dipped in the stuff, BUT DO NOT EVER dip flowering plants into anything!

After all the above .... remove the top layer of soil (till the roots) and check that there are no bugs/eggs under and replace with new soil.

Note:
Nicotine is a poison that disables the nervous system of bugs.

Boiling is a must, as it kills the "nicotine virus" – (TMV - Tobacco Mosaic Virus) and cooling will further irritate bugs as they like nice warm conditions.