Hi Melissa! I absolutely LOVE the Disney Dining Plan and was very excited to see that
T-Rex and
Rainforest Cafe were added to the list of participating restaurants for 2012! In my opinion, the
Disney Dining Plan is always a fantastic value and I never head to Disney without it!
To answer your first question, if you booked a vacation package through the Walt Disney Travel Company, including tickets, you are eligible to add the Disney Dining Plan to your reservation. This must be done prior to 3 days before check-in. If you booked through a travel agent, I would recommend you speak with that agency directly as their policies may vary.
And for your second question, You are absolutely permitted to "spend" table service Dining Plan entitlements at Quick Service locations, but please be aware that even though the table service credits are more valuable in a sense, they still only count as one entitlement at quick service locations.
All this Disney food talk is making me hungry! I hope you have a fantastic trip the to the Walt Disney World Resort, and if you have any more questions, please don't hesitate to let me know!