iPod software updates are meant to be installed by iTunes. If you are curious, you may extract sounds from it with File Juicer.
A ZIP file inside
The ipsw file contains a zip file inside. To extract it drop the ipsw file onto File Juicer. The zip files which comes out can be opened by double clicking it.
Extract Sounds From the iPod Firmware
Now you should have the actual iPod firmware file. Once again you can drop it onto File Jucier to give it a thorough search.
Out comes wav files which you can play with iTunes or QuickTime player. Ignore any mpg files - File Juicer just found binary data which resembles an MPEG stream.
Extract Images From the iPod Firmware?
The image data does not look as if it is saved in any standard file format. However there is compressed data extraced into the "other" folder - and this is could be image data - or sampled sound. The trouble finding the images is that there is no defining headers, which there would have been had a normal file format have been used.
Extract Stuff From the iPod Touch Firmware?
The iPod touch firmware is zip encoded, but inside this zip file are disk image files. These disk image files are either in a format not supported by Disk Utility, or encrypted with a password.