Welcome to TSF!!
Hi,
I would recommend that you take a look at
Windows Home Server. Without getting to technical on you, this is basically an OS that acts as a file server. A file server is different from a web server in that it only holds files, such as the ones that you have listed. It doesn't hold web pages or act as a webserver. It can hold all of your files and allow computer that has the software installed on it to connect to the server and then add or retrieve files from it. Since you are a small company it might be just the thing for you.
The website that I linked for you show a homeserver that is its own standalone computer. since you already have computer you can just get the Operating system and then install it on the computer. So don't get to worried that you need to get another computer.
Since I am primarily a Linux guy myself. I will get a hold of some of the windows folks and have them take a look at this post and see if they have any better ideas.
Cheers!