Hewlett-Packard and Acer have lowered prices of their netbooks as the back-to-school sales season kicks into gear in the U.S., offering bargains for users. Acer slashed prices on its Aspire one netbooks on Friday to as low as $329 for one version, while HP revealed new prices for Mini-Notes on its Web site . [ For more on products in the hot mini-notebook category, check out our …