There's no pre-made script available that can do what you're up to afaik.
If you know your way around in phpMyAdmin you could easily come up with a conversion script. Here's a sample a dump of SMF's members table:
INSERT INTO `smf_members` VALUES (1, 'admin', 1081202400, 201, 1, '', 1147361472, 'Admin', 0, 0, '', 'c823699a6f8080490862a12dadf22a3075a4bbe9', 'bla@email.com', '', 0, '0001-01-01', '', '', '', '', '', '', '', 0, 1, '', '', 0, '', 0, 0, 0, '', 1, 1, '172.26.17.126', '', '', 4, 1, '', 8, '', '', 6, 15549, '2f27', '', '', 0, 2);
INSERT INTO `smf_members` VALUES (2, 'tester', 1093298400, 4, 0, '', 1115995422, 'tester', 0, 0, '', '8e3a3e8f977f9a1b8902ea970e8b22b7', 'tester@some.com', '', 0, '0001-01-01', '', '', '', '', '', '', '', 0, 1, '', '', 0, 'foo', 1, 0, 0, '', 1, 1, '172.26.17.126', '', '', 4, 1, '', 6, '', '', 4, 438, '', '', '', 0, 2);
(with more data in it of course).
The dump of a coppermine user table will look like this:
INSERT INTO `cpg140_users` VALUES (1, 1, 'YES', 'admin', 'c823699a6f808sdf0490862a12dadhhhf22a5a4bbe9', '2006-09-11 19:12:49', '2004-12-09 17:33:32', '', 'user@some.com', '', '', '', '', '', '', '');
INSERT INTO `cpg140_users` VALUES (2, 2, 'YES', 'tester', 'dfhdfhgdfhgdfg', '2005-02-25 19:23:17', '2004-12-09 18:30:44', '6', '', '', '', '', '', '', '', '');
What we have is this: ID_MEMBER, memberName, dateRegistered, posts, ID_GROUP, lngfile, lastLogin, realName, instantMessages, unreadMessages, pm_ignore_list, passwd, emailAddress, personalText, gender, birthdate, websiteTitle, websiteUrl, location, ICQ, AIM, YIM, MSN, hideEmail, showOnline, timeFormat, signature, timeOffset, avatar, pm_email_notify, karmaBad, karmaGood, usertitle, notifyAnnouncements, notifyOnce, memberIP, secretQuestion, secretAnswer, ID_THEME, is_activated, validation_code, ID_MSG_LAST_VISIT, additionalGroups, smileySet, ID_POST_GROUP, totalTimeLoggedIn, passwordSalt, messageLabels, buddy_list, notifySendBody, notifyTypes
What we need (in coppermine) is `user_id`, `user_name`, `user_password`, `user_email` - just four fields, the rest could be empty (or rather: filled with default values).
Let's find the corresponding fields in SMF:
Coppermine field name | SMF field name |
user_id | ID_MEMBER |
user_name | memberName |
user_password | passwd |
user_email | emailAddress |
Now you'll just need to come up with a little PHP script that queries SMF's members table (SELECT) and writes a corresponding query (INSERT INTO) into coppermine's user table.
HTH
Joachim