Nebo,
It seems like we are talking apples and oranges and oranges and apples.
I am a little confused, because you talk about the users at first and then the physical computers. In your peer-to-peer network, you can have as many computers as you want connected, but the number of concurrent connections to any single computer (which would most likely be the one you have files or databases on) is ten. This has everything to do with the number of concurrent connections to the XP Pro OS after SP2 and nothing to do with the number of users and computers, etc.
Now, of course, the more users and computers you have, the more possible concurrent connections you have. From reading your post, you indicate that there would be (in the future) seven users if you are including yourself that would be accessing the system at anyone time. I would doubt that all of those seven would be accessing the XP machine at the same time. If so, then no one is taking care of the patients, physically, i.e. vital signs, etc.
So, you have room for three more users based on the above scenario.
XP also has a timeout set for when a disconnect happens. This can be reset to 0 which would allow for connections to disconnect more quickly, but I don't think you need to do this.
You are not on a domain, it appears you are on a workgroup. You are not logging into the "server," I believe you are logging into each individual computer which can all access shared resources on whichever computer you have designated as the "server."
A server/client domain running from Windows 2000 or 2003 server or Small Business Server (can't speak for Linux, etc.) are run on CALs. Typically, the Windows Server OS would come with five client access license, one for the server and four for clients. You then buy more in 5, 10, 15, etc. In this scenario, you can have 500 computers connected to a switch which is connected to a server with 10 licenses and you are fine, UNTIL they all try to log onto the domain. Then Windows takes first come, first serve. The fifth computer which tries to log on will not be allowed to. In this scenario, each computer which is logged on counts as a connection until they log off physically even if they are locked.
You never told us if you are using XP Pro or XP Home. This will make a huge difference. It would seem to make more sense if you were using the Home Edition as it can handle only five. In that case, then you may run into the "too many connections" problem. If you are using XP Pro, then there is an issue somewhere, possibly other peripherals that have connections. It is not always clear, and printers that are shared and in use can cause this to happen, which is where a print server would be cheaper than an NAS or server. In that case, get a good LaserJet printer or MFP that is networked and you should have less issues.
Finally, your decision between an NAS (if you are using Home and not XP Pro), depends on where you wish to go. If you just need to get rid of the problem, then a good NAS will solve your problem. If you are going to be adding more users and more computers, then you may wish to go ahead and set up a network which can grow with your business and go ahead and spend $2500 on a server and roughly $1200 to $1500 for an OS and CALs.
HTH
