Several issues here.
1) You are not using the correct method. That article is, "iTunes for Mac: Moving your iTunes Media folder". Your media folder is only part of your library. You need:
iTunes: How to move [or copy] your music [library] to a new computer [or another drive] - http://support.apple.com/kb/HT4527
Quick answer if you use iTunes' default preferences settings: Copy the entire iTunes folder (and in doing so all its subfolders and files) intact to the other drive. Open iTunes and immediately hold down the Option (alt) key (shift on Windows), then guide it to the new location of the library.
Windows users see tip at: https://discussions.apple.com/message/18879381
2) I suspect you are trying to copy to a NTFS formatted hard drive. If this was used for the PC then it is NTFS formatted. Macs cannot write to NTFS, but can read it. You will have to wipe the external hard drive and re-format it to a format both can read. FAT32 might work for an iTunes library.
If you purchased your music from Apple you can transfer it from your iPod. If it comes from other sources you cannot easily transfer it to the PC. You can use third party utilties to do this. Either way bear in mind this will just transfer your media files, again not the complete library. Most importantly it will not transfer your library.itl file which is what ties all iTunes together and has your playlists, ratings, date added, etc. You may also lose some artwork. Transferring just media is the equivalent to starting all over again with an empty iTunes library and adding files to it again.
If you have a FAT formatted flash drive you can copy chunks of the iTunes folder as long as you make sure it is all back together the way it was when you started.
If you really, truly want to transfer using the ipod:
Some of the information below has subsequently appeared in a document by turingtest2: Recovering your iTunes library from your iPod or iOS device - https://discussions.apple.com/docs/DOC-3991
Your i-device was not designed for unique storage of your media. It is not a backup device and media transfer was planned with you maintaining a master copy of your media on a computer which is itself properly backed up against loss. Syncing is one way, computer to device, updating the device content to the content on the computer, not updating or restoring content on a computer. The exception is iTunes Store purchases which can be transferred to a computer.
iTunes Store: Transferring purchases from your iOS device or iPod to a computer - http://support.apple.com/kb/HT1848 - only purchases from iTunes Store
For transferring other items from an i-device to a computer you will have to use third party commercial software. Examples (check the web for others; this is not an exhaustive listing, nor do I have any idea if they are any good):
- Expod (free) - http://www.headlightsoft.com/expod/ - Mac, universal for 104.+ (newer machines try de-Tune)
- deTune (free) - http://www.headlightsoft.com/detune/ - Mac, 10.5+
- Senuti - http://www.fadingred.com/senuti/
- Phoneview - http://www.ecamm.com/mac/phoneview/
- MusicRescue - http://www.kennettnet.co.uk/products/musicrescue/
- Sharepod (free) - http://download.cnet.com/SharePod/3000-2141_4-10794489.html?tag=mncol;2 - Windows
- Snowfox/iMedia - http://www.mac-videoconverter.com/imedia-transfer-mac.html - Mac & PC
- iexplorer (free) - http://www.macroplant.com/iexplorer/ - Mac&PC
- Yamipod (free) - http://www.yamipod.com/main/modules/downloads/ - PC, Linux, Mac [Still updated for use on newer devices? No edits to site since 2010.]
- 2010 Post by Zevoneer: iPod media recovery options - https://discussions.apple.com/message/11624224 - this is an older post and many of the links are also for old posts, so bear this in mind when reading them.
Syncing to a "New" Computer or replacing a "crashed" Hard Drive - https://discussions.apple.com/docs/DOC-3141 - dates from 2008 and some outdated information now.
Copying Content from your iPod to your Computer - The Definitive Guide - http://www.ilounge.com/index.php/articles/comments/copying-music-from-ipod-to-co mputer/ - Information about use in disk mode pertains only to older model iPods.
Get Your Music Off of Your iPod - http://howto.wired.com/wiki/Get_Your_Music_Off_of_Your_iPod - I am not sure but this may only work with some models and not newer Touch, iPhone, or iPad.
Additional information here https://discussions.apple.com/message/18324797