You can use a desk light with an economic bulb. The bulb has to be a "daylight" type one. Mine is a "Phillips Genie 18watt Daylight". Take
at least a 18watt light bulb (it 's the same power than a "normal" 100 watt bulb).
Otherwise, you can simply take your pics on real daylight, but not directly under the sun light. Another thing : ALWAYS disable your camera flash. It 's useless, you can't make good pics with a flash.
Last thing, if you use a desk lamp, you'll see that the natural light helps a lot for the pics quality. If you use the desk lamp at night, the pics are often too saturated.
You can find an excellent article (Darren wrote it) here to make your own light tent, BTW :
http://miniaturefootball.org/2009/12/30/1734/