Not much to explain there, really! Take your favourite song (AAC file), dump it on the thing and it shows up in iTunes under “Ringtones” afterwards. Now sync with your iPhone and you’re done. Oh, and make sure the song is not longer than 40 seconds max! MakeiPhoneRington is free! Direct download <–
Here’s a freebie which lets you change your Mac’s audio input and output devices quickly. SoundCheck lodges in the menu bar and sets your settings with one click. It also gives you the option to adjust the volume for output, input and system sounds. Thanks Rogue Amoeba! Direct download.