Here's one way to go about it:
http://www.dvcrequest.com/
I'll be totally honest, I've never used them, and can't vouch for their quality or honesty, but they do seem to have a goodly amount of testimonials. They do a good chunk of the work for you, and charge $13 a point. Now, I've heard of individual dvc owners, on their own, maybe on other disney fan forums, maybe through ebay, and they're only charging 10-11 a point, which would be cheaper, but then you're doing more of the work, with no one to help you if the owner who agreed to rent you their points flakes out. It involves a little more trust. At least with this website, or another one like it, you might have some recourse, someone to gripe to, if the deal goes south.
As far as how many points you'll need for your vacation, that will depend on various factors - time of year, length of stay, the resort you choose and the type of room (studio, 1BR, 2BR or Grand Villa). If you wanted to stay at Boardwalk Villas, or Animal Kingdom Villas, there are also subcategories based on the view. But the above link also has a point calculator, which will let you know exactly how many points you'll need. Type in your preferred check-in and check-out dates, and the resort(s) you're interested in, and you'll get the numbers you need. Multiply that number by 13, and that's the dollar amount you need to rent through that particular company.