I am new at this....

I am trying to render for a small screen like an MP3 player.
When I use the following profile...
f=avi vcodec=dvvideo pix_fmt=yuv420p acodec=pcm_s16le s=360x288 profile=dv_pal
It produces a small file that doesnt work.

The following standard profile works great
f=avi vcodec=dvvideo pix_fmt=yuv420p acodec=pcm_s16le s=720x576 profile=dv_pal
but produces a large file.

can someone help me figure out what size to use with AVI for a small screen?

The profile dv_pal will only work with 720x576.
Try using another format and set the resolution via the rescale option (below the format list).

Also, a MP3 player can not play DV. You need to figure out what formats, resolutions, frame rates, and bitrates your player supports. Then, someone might be able to help.