The second method is to load a program on the computer that will emulate an AirPrint compatible printer. In general those apps will probably have the best results, quality wise.

Several printer manufacturers have their own apps for their printers. It may still work with iOS 4 if you get it before the app is updated in the App Store. Print n Share used to be able to print from AirPrint enabled apps if it was loaded the background. Most (or all) other print apps can only print pictures and/or files that have been copied to that app via Open In or other method. One is to use a printing app on the iPad. Of course some of us already have printers and do not want to buy a new one. If you get this kind of printer you can print directly from within apps that support the feature, which is many. These are usually available on the manufacturers site. Some printers may require a firmware update to work. If you want this feature be absolutely certain the printer supports AirPrint before buying. Some printers are directly compatible with AirPrint on the iPad.

It does not look like the Canon MX410 printer is on the list of AirPrint compatible printers.

Canon mx410 printer driver