Excel could be saved as a CSV. If that works for you then you could use:
$fp = fopen($complete_path_to_the_uploaded_csv_file, "r")
while (($line = fgetcsv($fp, 1000, ",")) !== false)
{
// $line is an array of cells for the current line in the file
// do something
}
There are other examples here:
http://ca3.php.net/fgetcsv
