OK - I will give you a QUICK little blurb:
The first thing you need to decide when doing a planted tank, is what "level" of lighting you want to work with. There are 3 "kinds":
1. Low Light
2. Medium Light
3. High Light
How much light you have is known as watts per gallon (WPG) - and that will determine if you have a low, medium or high light tank... now of course there is different light spectrums to get... but thats a lot to learn at first and i wont get into that, just wanted to mention it so you are aware.... also, keep in mind that high light tanks are very intense - they require c02 (in most cases), fertilizers, etc. etc... so i do not recommend that as a first tank...
Something else to keep in mind (when shopping for plants) - plants are rated for a certain lighting level, so for example you cant put a high light level plant in a low light environment and expect it to survive...
Substrate... there are a ton of different kinds of substrates, flourite is common - and very good - i use it in my 125.... but if you want to get into "planted garden of eden" type aquariums, id suggest something like this:
http://www.aquaticplantcentral.com/...-mineralized-soil-substrate-aaron-talbot.html
next thing - fish.... seriously consider what you are going to put in this tank.... large schools of fish, some plecos, etc. can do damage to your plants... so you want to make sure that the fish in the tank are "plant friendly"
Last piece of advice,
http://www.plantedtank.net/forums/ is the most knowledgable, friendly planted tank site i have come across - i highly recommend them
Em