Saving an existing word document to Sharepoint

Solution to the following problems:

"while i am trying to save the document using save as dialog box,unable to save it to document library.but instead it is getting saved under my documents folder"

"UNC Path of SharePoint Document library not valid"

"We have a user that is having issues with word documents in document
libraries. When she opens a Word Document on SharePoint site and makes
changes to it and then wants to save it back to SharePoint document library,
she is getting prompted for "MyDocuments" on her personal C drive instead of
being provided the path to the SharePoint document library. The user has
Windows XP SP2 and Office 2003 SP2 installed on her machine. She has also
added the Sharepoint site as a trusted site to IE."

The Solution:
•On Windows Server 2003, set the WebClient service startup to automatic, then start the service. You may need to reboot the server for this to fully take effect.

•On Windows Server 2008, install the Desktop Experience feature, then restart the server.

Problem:
"The Folder is no longer available. The web server is busy. Please try again later."
Solution:
Issue turned out to be the ISA server - if you ensure that your Sharepoint Site is excluded from the ISA, you should find the issue disappears!
The issue could also with users using VPN.