Just like Wildfya said, adding CO2 means getting good ferts, good lighting, and good substrate. Carbon is probably the limiting nutrient in your tank (it is for the majority of tanks) but if you inject CO2 w/o supplementing the other nutrients [mainly P, N, K, Fe (especially for your sword) and other traces] then you now become limited by one of those. Then you have to have pretty good lighting, for the plants to be able to utilize the nutrients. I'm by no means saying don't inject CO2 (either by pressurized, DIY, or Flourish Excel). I'm simply stating that IF you get into the CO2 injection, be prepared to keep an eye on the other nutrients. I also am a big fan of fertilizers from gregwatson.com . You can get about a year's worth of ferts for your tank (looks like a 55gal) for under $25 shipped (rough guess). Alot of this will depend on how involved you want to get with this, as well as what plants you want to grow.
There are quite a few plants that do just fine with normal comes-with-the-tank fluorescent bulbs, a little bit of fertilizer and some Flourish Excel 2x a week. Other plants require 4+ watts/gallon of compact fluorescent (or better) lighting, alternating fertilizer schedules, and continuous CO2 injection.