to have exact max values of the tosh 800, look on the forums at
www.corecodec.com for PocketMVP encoding.
basicaly you can try small clips of like 10 minutes or something by trial and error method.
on a 320x240 screensize my Ipaq2215 can play around 300kbps video and 32kbps audio (mono) at a good speed, meaning you can use any video and audio bitrate combination as long as you dont go over 332.
PocketMVP has some stuff in it that can make use of the graphics chip in your tosh, meaning you can prob go higher.
but if you do a proper encoding, you can hardly tell the difference when higher then 300 for video.
www.bigdsvideo.com has excelent guides on DiVX encoding,
you can also have a look at my sig,
and of course the corecodec.com forums has additional info and recommendations.