You could probably create a big SQL query and run that, but it'd need a lot of code for 60 users to fill all the fields in the table. It is probably possible though... hardest thing would be settings the password encryption with the hash but I could tell you how to set all their passwords to 'test', then they can login and change it...
It'd be easier to just get them to register themselves though.
Edit: Try this... maybe in a test environment first...
INSERT INTO mybb_users (uid,username,password,salt,loginkey,email,postnum,avatar,avatardimensions,avatartype,usergroup,additionalgroups,displaygroup,usertitle,regdate,lastactive,lastvisit,lastpost,website,icq,aim,yahoo,msn,birthday,birthdayprivacy,signature,allownotices,hideemail,subscriptionmethod,invisible,receivepms,pmnotice,pmnotify,remember,threadmode,showsigs,showavatars,showquickreply,showredirect,ppp,tpp,daysprune,dateformat,timeformat,timezone,dst,dstcorrection,buddylist,ignorelist,style,away,awaydate,returndate,awayreason,pmfolders,notepad,referrer,reputation,regip,lastip,longregip,longlastip,language,timeonline,showcodebuttons,totalpms,unreadpms,warningpoints,moderateposts,moderationtime,suspendposting,suspensiontime,coppauser,classicpostbit,loginattempts,failedlogin) VALUES ('2','Test','098f6bcd4621d373cade4e832627b4f6','','KPVsshKOmBRJhZkdjLRp93S5vRFeEIsEK9qgpFqeQVJ5SGPAKs','[email protected]','0','','','','2','','0','','1229004939','1229004939','1229004939','0','','0','','','','','all','','1','0','0','0','1','1','0','1','linear','1','1','1','1','0','0','0','','','','0','0','','','0','0','0','0','','','','0','0','','','0','0','','0','1','0','0','0','0','0','0','0','0','0','1','0');
Change the entry of the UID for each (the first entry in the brackets in the code, '2'), making sure there are no duplicates, and change the username of each (the second entry in the brackets in the code, 'Test'), making sure there are no duplicates. Also make sure your table prefix is correct. Leave everything else as it is. This one line (it is just one line in SQL terms) will create a user with username 'Test', UID of 2, and a password of 'test' (which is encrypted so you can't see it here).