[Kolyaj]

var data = [];
'Username:1hfjdjdk<BR>Password:ahdgdgdg<BR>Username:1hfjdjdk<BR>Password:ahdgdgdg'.replace(/Username:([^<]+)<BR>Password:([^<]+)/g, function(match, username, passwd) {
    data.push([username, passwd]);
});
alert(data.join('\n'));