сделал так:
var fso = new ActiveXObject("Scripting.FileSystemObject");
var ts = fso.OpenTextFile("logs/"+ rtrim(xmlUMKbaseconfig.documentElement.getElementsByTagName('umk_name')[0].text) + ".txt");
var result = new Array;
var i = 0;
while (!ts.AtEndOfStream)
{
var r = ts.ReadLine();
var x = /\d+(?=\%)/.exec(r);
result[i] = x;
i++;
}
ts.Close();