Try this free program someone on here posted a while back called Easy Thumbs. http://www.fookes.com/ezthumbs/ . This program is great for making mass thumbnails, but you should also be able to use it to adjust your photos to the same size.

OK Thanks ... Just tried it threw them in and wanted 540x540. They still come out with a a few pixels difference.
Done it. Changed setting from "best fit" to "stretch to fit" on ezthumbs..... Handy little program.