Sharing files between Windows and Ubuntu is often necessary : here's how to do it !
7 Tutorials published a well detailled tutorial on how to share files between a computer on Windows 7 (aka Seven) et Ubuntu.
For more information, you can read the Ubuntu-FR documentation (in French).
Sharing folders used to work fine between Ubuntu 7 and Ubuntu is now hit and miss. And I got the same troubles with a Windows XP workstation: I assume Micr$oft changed its protocol to force Windows XP workstation migration ... as these are not supported, they don't benefit from any updates. The Ubuntu-FR documentation (in French) states there's a modification to be done in the registry on the Seven server to share files with Ubuntu machines ... however that did not work for me !
In the end, I used a NAS that was badly used in the company.
Happy sharing ! !