The safest way to connect either way is via VPN. I suggest you contact your
local system admin and ask if they run a VPN service so you can login to the
company network from home free from security worries. Ask them how to use it.
If they do not run such a VPN service - they should - as the company's security
is at stake.

Look at where you preset your IE settings, copy them down and from Ubuntu using
Firefox, Edit, Preferences, edit the settings into the Advanced tab, Network
Connection settings.