For starters I would suggest heading to rexgrigg.com for a good overview of planted tank basics.
I suspect your current lack of success with plants is due to insufficient lighting. Most commercially available canopies don't provide nearly enough lighting. You will need about 110 watts over your tank to provide 2 watts per gallon, which is probably the minimum to grow plants. You may be able to grow some plants under this amount of light, but you have to choose them carefully. There is a plant gallery here, as well as one at plantgeek.net which lets you know if a plant is difficult or requires high light levels.
Temperature, aim for 76.
CO2 will help with plant growth. You can use the yeast method to provide CO2, but in a 55 gallon it may be hard to provide sufficient amounts. However, some CO2 is though to be better than none. Here is a link that will explain: http://members.cox.net/tulsaalstons/...Pressure%20CO2
Substrate: a lot of us here use specialized substrates. This can get expensive for those on a tight budget. Again, you can use plain gravel. You just would want to choose plants that are not heavy root feeder. Java fern comes to mind; it will do well under lower lighting levels as well.
Most of us here use cannister filters. Undergravel filters are generally best avoided in a planted tank. Power filters will suffice but anything that causes a lot of surface aggitation will cause excessive loss of CO2.
That's a start. I am probably not the most qualified person to answer as I really (within reason) went all out on my tank but I see where you are coming from, I was a poor student once. And I will never eat another frozen beef pot pie and Mr. Noodle again .