The dining and reservations website is part of the main Disney site
http://disneyworld.disney.go.com/reservations/dining. The website has several great features. First, you can browse the many dining establishments located throughout the resort. The site can be searched by location, such as the Magic Kingdom, or by cuisine, such as Asian or Italian. Second, there is a brief description of each dining experience, including price ranges for table service restaurants. Finally, and most importantly, the website allows you to make advanced dining reservations up to 180 days in advance. Amazingly enough, you have to get ADRs six months in advance if you want to eat at some of the more popular spots, such as Le Cellier in Epcot's Canada pavilion.
In summary, the Disney World dining & reservations website is a helpful tool both in the planning stages of your vacation as well as while you are actually there. I certainly recommend making dining reservations as far in advance as possible, but as a last resort the mobile phone version of the website is a great option. Bon Appetit!
Have a Disneyriffic day and remember to keep moving forward. See ya real soon!