Flash Cart?

Hi, I am new to the whole emulation thing, and well, the DS its self. I need to know what is my best value as of now...
I currently (as of yesterday) own a DS Lite. I have heard of many different movie players for it that play music and view Jpeg's too. But I am not sure exactly if I should get one of those or a Flash cart that i have been hearing about over and over again... I mainly want to watch movies, view pics, listen to music(mostly), put many, many, apps on it and maybe put a little game or two on it. But thats all. So I am asking you, Should I get a flash cart (what ever that really is), or A movie player?
If I was to get one or the other, which one is best for me (in terms of Mb/Gb, value, price, quality, etc.)
PLEASE HELP ME in my decision! THANKS in andvance!:D