I have all of my apps and music on a external hard drive so I'd like to be able to add/remove content on my home PC and my work one too. I've looked all over the net, and even tried some of the suggestions, and it never works
You can do it but it is a major pain to set up but once you have it running it works great. I have set up 3 computers (1 Mac and 2 PCs) that allow me sync music/videos to my iPhone.
HowTo
http://www.andrewgrant.org/2008/03/30/how-to-sync-an-iphone-with-two-or-more-computers.html
You can also use this program to transfer media content to and from any iphone.
http://www.xilisoft.com/iphone-transfer.html
What in particular are you trying to synch?
See I have my library moved on my home computer but for some reason when I plug the external into my work machine, and try to point it to the same place, it doesn't work?