You are referring to the Digital Transition occurring February 17, 2009. No, you will not have to purchase a new TV to view programming after the Transition occurs. The people most affected by the Transition will be those who rely on free over-the-air broadcasts, or use "bunny-ears" to receive their programming. In this situation, the viewer will need to purchase a digital converter box. If they are unable to afford the box, they can apply to receive up to 2 coupons worth $40 each to put towards the purchase of converter boxes. This coupon program is funded by the Federal government, and those needing to apply can visit https://www.dtv2009.gov/.
If you have satellite tv programming, such as Dish Network, you will not be affected. However, if you want to receive High Definition digital programming, you will want to get in contact with your provider to make sure you're set up with the right equipment.
If you subscribe to Cable TV, you will want to check with your provider to make sure you have the right equipment.