Microsoft is once again attempting to gain ground on Google while tempting Web users with frequent flyer miles. You can earn miles with the programs of American, Delta and US Airways for frequent Web searches now through April 15, 2009. The kicker is that you can only get the miles if you surf using Internet Explorer–Safari, Firefox and others won’t work. The online program, called SearchPerks, is available for Web users who have a Windows Live ID and software downloaded from the SearchPerks site and who use Internet Explorer 6.0 or later. You can collect a virtual “ticket” for each search you make, up to 25 per day. You can then exchange the tickets for miles or other prizes. You can exchange 1,800 tickets for 1,000 airline miles, 3,400 tickets for a cookbook or 525 tickets for five music downloads, among other options. The promotion is limited to the first million U.S. residents, 13 years old or older, with a Windows Live ID and who sign up before Dec. 31, 2008. But don’t expect to earn enough miles for a free ticket. Even with the current 500 point sign-up bonus being offered, it would still take you four years and 320 days, searching 25 times each day (the limit to earn tickets) to collect 25,000 miles–and remember, the offer ends April 15, 2009.