Your television may have the ability to show 720p HD video, but you fail to mention what you want to play this disk on.
Regular dvd players can normally only read certain resolutions. They are almost always limited to those found in dvd-specifications. So, if you are in the US and have NTSC specs on your dvd player, the highest resolution it can read is 720 x 480. There may be some divx compatible dvd players that can handle higher resolutions in avi files encoded with xvid or divx, but if they exist that is beyond my experience and knowledge.
Some dvd players can upscale their output and produce a better looking picture, but the disk itself has to be SD resolution.
If you have a blu ray player you can make an AVCHD disk or Blu ray format video on a regular dvd or a dual layer dvd and use higher resolutions.
So, if you want to play this on a regular dvd player, you should convert to dvd-video format at 720 x 480 if you are in the US. (720 x 576 for PAL countries). Look at programs like FAVC, DVDFlick or AVStoDVD for this process. All are free and produce finished dvds ready to burn to disk. If you want to try a commercial product, ConvertXtoDVD is popular around here.
By the way, what are the specifications of this video you have? Open it with MediaInfo or Gspot video utility (both are free to download and use). These will tell us the resolution and codecs used in the video now.