virtualbox.org

There is no guest additions that will work with Windows NT 3.51, so I am wondering how to move files to it. I want to use a different video driver, and a different email client. I tried to email myself, but the native "Outlook Express" will not work with any of my email accounts, even with the ssl checked. The browser is kind of hopeless on many download sites too. My host is a Lenovo T61 laptop with Windows 10 installed.

A standard network share would be option #1.

Otherwise, FTP would of course work, though a real PITA to set up/

If you just want to get a bunch of files in there as a one off: bundle them as an ISO and attach as a CD.