Is open source and stable. Perhaps that would do the job.

You can dual boot different versions of windows: http://windows.microsoft.com/en-us/windows-vista/Set-up-a-dual-boot-system-from-Windows-Vista-Inside-Out -- Maybe you could have an unencrypted partition to boot off of at home, and an encrypted partition to boot off of at work. Or boot windows off of a flash drive: http://articles.techrepublic.com.com/5100-22_11-5928902.html Although I might suggest linux. Ubuntu's full disk encryption works great. You could set up a fully encrypted usb stick to boot from @ work.... If they accept that encryption. You could dual boot Ubuntu with windows. Just some thoughts.

http://en.wikipedia.org/wiki/WASTE might work, it was developed by Nullsoft for internal communications and file sharing, is encrypted, and has no central server.