Plant newbie...help!

It depends what you want to do. If you want to get your wattage as close to 3 as possible you can work on high light plants. They need fertilizers but you can order them in a dry, powdered form from www.gregwatson.com

If you go the cheaper route with low light plants your selection will be a lot more limited but you may not have to add ferts quite as often.

Hornwort, Javamoss, Java fern, anubias are good for beginners in a low wattage setup as well as many others. You can always check www.aquariumplants.com under beginners for a good idea of what you can get. It'll tell you their needs as well.

Grundy: I believe planted aquariums can be quite a plunge financially. Especially once you start messing with bigger tanks. Like twig mentioned, if you stick with low wattage lights you will be very limited to the type of plants you can grow. You should aim for 3 watts per gallon. However, keep in mind that with that amount of light you will need CO2 and micro/macro nutrients to battle persistant algae. A pea sized substrate is OK for most plants but you will much healthier plants with smaller "specialized" substrates. Keep in mind though that you will again limit yourself to the type of plants you can use if you decide to go with your existing substrate. You will have trouble keeping a "carpet" plant such as hairgrass or glossostigma. I highly recommend Eco-Complete as I have had GREAT success with it, but some other popular brands include ADA and Flourite. These substrate usually come packed with all sorts of nutrients to begin and maintain healthy root growth and often look more natural then other substrates.
As far as fertilizers, I use the Flourish line of products... (flourish, potassium, nitrogen, phosphorous, etc.) I stay away from Excel as it tends to cause melting on some plants (especially crypts). All have worked well for me.
The beginning can usually get a little pricey but the reward far surpasses the expense. There are a ton of benefits over having real plants such as more oxygen in the water. Plants help reduce waste and therefore, depending on stock, reduce maintainence. You're fish will behave in a more natural way as you will provide them with a natural envirnment. If you have any more questions don't be shy to drop me a line buddy, GOOD LUCK!

Well, a 10 gallon aquarium would be much easier on the wallet as you can resort to more do-it-yourself items. A 10 gallon tank would need 25-30 watts which shouldn't be expensive. You will need about a bag and a half of substrate (2 1/2 to 3in) instead of 13-15 bags. You can easily build a DIY co2 system with a 2 liter bottle, some air tubing, yeast, baking soda, sugar and some type of diffuser, such as a ladder, bell, or a favorite of mine, the Might Momato Glass Diffuser (scroll to the bottom). Keep in mind water quality when adding Co2 as Co2 naturally lowers pH and can cause a crash if your KH is not in line. To answer your fert. question, I use Flourish, Flourish Potassium, Flourish Phosphorus, Flourish Iron, Flourish Nitrogen and have had nothing but success. I placed Flourish Comprehensive root tabs into the gravel near plants that are heavy root feeders and have seen intense root growth... Hope that helps, if you have anymore questions on water parameters or anything else for that matter I'll do my best to help.

One thing I forgot to mention, be sure when purchasing bulbs that you go for something with a heat range of 6000k to 10,000k. This is optimal heat range the plants use.

I think those are good first steps. A good substrate will really improve the health of your plants and a light will provide them with the energy to grow and produce oxygen. You can visit this site for some DIY and non expensive lighting options. Co2 is not a necessity but with a good light (30watts) you will not see much benefit without co2 and algae can become a problem. You can daily dose Flourish Excel but remember that if you plan on crypts, they will melt. I strongly suggest a diffuser, such as the one I posted belows or even a hagen ladder. Another option, since you are using HOB filters is to break a part of the strainer so you can fit the airline tubing into the intake of the filter, it will get disolved by water movement. Remember co2 is not hard to generate and if you are interested I will give you a home recipe of mine as well as some instruction on making an air tight container (not hard at all).
As far as your plant choices, Java Ferns and Moss does better when it is attached to a piece of driftwood instead of burried in a substrate. Excuse the rant but when starting out, I suggest a nitrate test kit that is easy to use as you will be testing quite often in the beginning to figure out your dosing regiment. I keep my nitrate around 15ppm. If your nitrates drop the algae outcompetes your plants for nutrients and will eventually starve them. Cyanobacteria is can form from nitrate difficiency since it will feed off the nitrogen in the air. I use Flourish Nitrogen to get my desired nitrate reading. With high light, injecting co2 will also help fight algae. In addition, you can add more fast growing stem plants to use as much of the nutrients as possible while your tank naturally establishes. You can use plants such as Cabomba or hornwort. With 30 watts of light you can also add some amazon swords and crypts. Just remember, crypts will melt if you dose Flourish Excel. Let me know if i confused you hehe or if you have any more questions.


EDIT**
Hey, just did some looking around, the 1x36w is a good option for under $50. You can either modify the "stock" hood or purchase one of their finished hoods for another $30. Here is the bubble counter/diffuser that you would need to diffuse co2 into the water. Like I said, co2 can be produced by putting sugar, yeast, baking soda and water into a bottle of juice Let me know if there's anythign else I can do.