Here's some exciting news for those of you who have an iPhone and want to have the Star Wars Imperial March play every time your mother-in-law asks you for help installing the latest sudoku game: with a bit of file-extension tweaking and judicious use of the new iTunes 7.4 for Windows or Mac, you can now customize your ringtones without having to donate another 99 cents to Steve Jobs' favorite retirement fund.

Courtesy of MacRumors and Gizmodo the process is quite simple. On either a Windows or Mac machine, manually duplicate any AAC file in your file browser, rename the extension to M4R, then add it to your iTunes. In iTunes, go to the ringtone section of your iPhone and your new 'tone should be ready to use as soon as you synchronize the device.

There are step-by-step tutorials available, including one with screenshots for those visual learners in the class.

Two CNETers gave the workaround a try on their personal iPhones--for some reason, we don't yet have a iPhone--and it worked for them. Let us know in the TalkBack section below how this extension swap works for you, or if you have any other favorite iTunes tweaks. We'll feature the best in an upcoming post on the Daily Download.

Perhaps not coincidentally, this process is nearly identical to getting MP3 or AAC tracks to show up in your iPod's directory as audiobooks. Once you've converted the MP3 or AAC to M4A within iTunes, you go to the new M4A file, change the extension to M4B, and then load the new M4B file into iTunes. Once synched to your iPod, it'll show up in the Audiobook directory. Yes, it's not directly relevant to the iPhone, but it's good to know that your iTunes and iPod are far more customizable than Apple would like you to believe.