Transferring sha1 passwords to md5

I created a Ruby on Rails recipe site awhile back, and it uses sha1 encryption for the passwords. Is there a module or simple way of making these passwords work with Drupal? Is it as simple as adding a salt field in the user table and switching all instances of "md5" to "sha1" in the user files?

If it's not possible without a lot of behind-the-scenes work, how would you suggest I go about resetting the passwords of 80+ user accounts? Is there a way for me to bulk reset passwords and have emails sent out with new passwords?

Thanks in advance!