HOLD IT PLEASE! Putting it on the DSL is a BAD idea based on what your saying here:
"We have 5 computers on our network, one is used as our main upload server. Our connection speed sits at about 1mb/s, which is awful because I do a lot of downlaoding/uploading of very large image files for editing. "
Your comment "connection speed sits at about 1mb/s" I am guessing your meaning Internet connection correct? That has nothing to do with you sitting in your chair, and trying to access the upload server by the closet in the same office (you said it is on the same network, i.e. is sitting in the same physical space as the other 4 computers).
First if you have the 5 computers on the network all in your office/house, are they all connected? Wireless? Wired?
If the server is wireless make it a wired connection unless your running 802.11ac . A wired connection is normally 1Gbps between that connection and any other 'connections' on the router (no Internet involved here). The other 4 computers can be wireless if you wish (maxing out at 400Mbps on N with no one else doing 'anything' through the router) but you may wish to put the primary workstation (the one your editing very large image files from) also Wired. So it can communicate to/from the server at 1Gbps.
Now if the other '3' computers are for other uses (people Youtubing etc.) you can enable QoS (Quality of Service) on those computers and the router. Then setup the router Priority that ImageWorkstation / Server have the 1st priority over everything else. Even with them both on 1Gbps connections, if the other 3 computers are demanding to all watch the new episode of First Blood on NetFlix from the Internet, that will still impact your 1Gbps connections as they pass through the router.
Best if you specified if your using FTP to the server or what software / how your uploading / downloading to/from the server.
This gets me back to the next segment, your trying to have a 'Network', that means file sharing, print sharing, etc. If your doing the "one is used as our main upload server" as a off the shelf Window 7 PC, then it won't be designed specifically to work as a file server, and be doing all sorts of other things which can also effect your Upload/Download. If you have need of a Server, then you need Windows Server, either 2008 or 2003 or setup a simple (much cheaper) Linux Box with FTP serving. You don't need to create a 'Domain' perse, where each person needs to validate authentication to access a computer or network resources, but your heading in that direction already since you want to know 'who did WHAT!!! to the image files when?!??!?!' and have some level of control and authorization (don't want Becky's Cuz who surfed Porn on her computer to infect the 'server'). You might want to reassess what your currently doing, and what you plan to affect you over the next 24 months (hire three more people and boom you are going to severly impact productivity for numerous reason).