javad,
s1fwx does not work on Win98 you need Win2000 upwards.
As "bsaylor" has mentioned your memory chip may only be 512MB. If you have copied almost 2GB of files to your player try copying some of the last files back to your PC, you will most likely find they are corrupt and unplayable. There is no fix for this you need to take this up with your supplier.
Using Bitdefender and Avast I have had no anti virus warnings from 3.68 or any other version of MP3 Player Utilities.
If your players LCD is 1.5 then full screen will be 128x128, if it is 1.8 LCD full screen will be 160x120.
To find the settings of your test video, run the video on your PC using AMV Player and while it is running right click on the picture and select properties and it will display the size and frame rate.
The best way to adjust your videos is to convert all your files to AVI before converting them to AMV. This way you can crop, resize, adjust volume if needed, adjust brightness and contrast what ever you prefer to get the desired AMV quality.
Some free conversion programs are PocketDivxEncoder or VirtualDub. You will find information on some different methods that people have used to obtain good results in the Video Related Forum. "Vegas215.com" posted his findings
HERE
Hope this Helps
