Hello zshan, and welcome to the forums.
First off, does your car dvd player support playback of mp4 files without conversion to dvd-video? Look in the manual for the player and see if it does, and what specifications are needed in the mp4 file. Normally, you'd just need to burn these as data if the player supports mp4 files.
Next, we'll move on to dvd-video. PAL or NTSC standards would only apply to dvd-video, and vary depending on where you live. Most of North America uses NTSC standards, while most of the rest of the world uses PAL. What program have you used to convert the mp4 files to dvd-video?
If you need to convert mp4 to dvd-video, I'd suggest a free program called AVStoDVD. Here is a guide for using it: http://club.myce.com/f32/avstodvd-guide-331620/
To do the actual burns to a disc, I'd recommend ImgBurn. Use good quality discs, like AZO Verbatim, or Taiyo Yuden, and burn at a moderate speed. If you need more detailed instructions on the burns, we can provide that.