It's actually really easy.
1) Export the Excel file as a CSV (text-file) with comma breaks.
2) Open the text file in something like BBEdit and append commas to the beginning and end of every line.
3) Via the command line, or a utility like
phpMyAdmin to import the text file, using the commas as field delimiters into a pre-existing table.
It's fun.
As Rower_CPU said, this. I will go into a little more detail.
I do this all the time, as I have to export a list of MS Exchange contacts to Excel, then save as a CSV and import into a MySQL database for a PHP program I wrote to do mass mailings.
You will need PhpMyAdmin for this. You can google it for instructions to install it, or it also comes with many bundles, like XAMPP (available for Mac).
If you have the file opened in Excel, save the file as a .CSV. You don't need to add more commas to it (At least from Excel in Windows). In PhpMyAdmin, select the database and table you want to add it to (create it with the necessary columns if you need to), and click the Import tab. Browse to the .CSV file, and select the "LOAD DATA" option (I've found if you dont select this, sometimes the first row doesn't get imported from a CSV). Click to import, and if your MySQL DB columns match the fields in the CSV, you should be good to go.
Alternatively, if you are using MySQL and understand PHP, you could write a script to parse the XML file and use INSERT to populate the database. This would also let you add additions in the future without needing PhpMyAdmin.