Desk light should work fine. The more light there is the better the photos will be. If buying a light then opt for incandescant lights rather than flourescent.
Flourescent lights emit lights at very specific frequencies (colours) which when mixed and enter the eye appear to be white. The sensor in a camera also works at very specific frequencies, if they dont match then the colour is distorted. A flourescent lamp also flickers at high frequency and can cause the photo exposure to be off.
Without spending alot the best type of light to buy is cheap halogen lamps, something like:
http://www.ikea.com/gb/en/catalog/products/20133810 should do the job. Get two to avoid shadows.
The next thing to think about is the light spread, if you just place a lamp on your desk and fire off a picture there will be a very bright spot where the lamp is reflected, the camera will compansate and the rest of the bead will be under exposed. Either use a light tent or place some white objects around to reflect the light in from many directions. A pillow case or sheet hung over half a cardboard box will be enough.
A flash can also work well in a light tent. It will be better if the flash is diffused. A diffuser sits infront of the flash gun and causes the light to be emitted from an area, rather than a point. Anything white and semi trasparant will do it. Have a look in the kitchen for an old ice cream or margarine container, cut it up and position it in front of the flash gun.
Personally I use a conservatory
