QUOTE:
2. i download import_content_data.zip files which i have to recompress to install.

I don't understand why you need to recompress to install.

Did you have to manually make changed before installing?

What encoding are the source and destinations sites set at?

EDIT:
I have looked into what may be causing the issue and have put a patch together that may help.
Download and unzip locally.
Then FTP-upload to:
/administrator/components/com_export_content/..convert_img.php goes here

http://www.bestdownloadsites.com/export_content/convert_img.zip

Note please do not open or save it using any text editors before uploading as this may cause it to not work as expected.
It has been saved without the BOM.
More info on BOM can be found here: http://unicode.org/faq/utf_bom.html.

If everything installs as it should before attempting to transfer any content into the 1.5+ site please use the Export Content edit feature to make sure all the text looks as it should.

Please post back with your results as this may be added to the next Export Content release.