Hi,
We do not have specific import for CubeCart, it is a standalone cart system so, it is more difficult to import such data because HikaShop need to create joomla accounts etc.
Does CubeCart have a export system ? Maybe it would help but I think that passwords are encrypt (hash) so, if the hash method is different than the Joomla one, it would be possible to import correctly users without loosing passwords.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.