Joomla - clone user on register

I'm looking for a way to add Joomla user to custom table (PrestaShop - same database) - duplicate user on registration. So user will be able to login to Joomla 开发者_C百科and second script (PrestaShop) using same login information. Any ideas where I should start looking in Joomla files? I know, that custom user plugin will be a better way to achive user duplication, but now I'm looking for temporary hard-coded fix until I'll be able to write a plugin.

(Joomla 1.6)

The other solutions won't let you save the passwords. If you are looking for saving the password as well then you will need to look into

components\com_user\controller.php function register_save() {}

Note: I have given with reference to joomla 1.5. It might slightly vary if you are using joomla 1.6