In short, a planted tank requires quite a bit of care that should, if possible, be planned on beforehand.
Lighting. A minimum of 2 watts per gallon is recommended, depending on the type of plants. Some can thrive on much less, some require more. So, with normal flourescent tubes, you'll need about 160 watts of total light.
Fertilizing. Most tanks will require fertilizing. For a beginner, I'd recomend Kents, or Seachem Flourish, used according to package directions.
I'd also recommend that you subscribe to rec.aquaria.freshwater.plants. There are many aquatic plant enthusists there that have years of experience on me. Also, read
http://faq.thekrib.com/plant.html .
hth