Looking on zen cart forums, there is apparently a tool called easy populate which allows you to export your product data into a CSV:
www.zen-cart.com/forum/showthread.php?t=87881
Then, you can edit it via excel and change the column names to match the ones in HikaShop and then import it into HikaShop.
If you want to knwo to list of available column names in HikaShop, you can go in the import screen and enter some crap in the textarea and click on import. That should display an error message with the list of valid column names.