Start by reading everything in the newbie guide.
Covers just about everything you've asked.
https://bitcointalk.org/index.php?topic=9430.0Your video card is the most important part of the equation ( the gpu anyways )
Ati is heads above Nvidia for mining.
GUIminer is probably the easiest program to start with.
You'll certainly want to read the above mentioned guide, while you might be able to just run the miner and it works,
most of the time there will be additional changes you need to make to see it all come together.