pulling my hair out trying to connect to an XP share

Rule one on sharing anything with XP (and Windows without ActiveDirectory) is: The worgroup-name has to be exactly the same!
Rule two: Does the user accessing the folder has the appropiate rights to at least read? When in doubt give the "user" everybody every usage right.
Rule three: Have you restarted the XP-Machine and the system accessing to the share? I'm everytime suprised that a simple restart kills most of the problems in this area.

other Points to consider:

• some folders on C:\ aren't advicable to share. The whole C:\ outside C:\users (or C:\DocumentSetting or how the userfolder was titled in XP) shouldn't be shared. More security pains then any gain worth doing it.
• using an old XP-System as a FileShareServer in a HomeNetwork was and will never be a good Idea. XP isn't made for handling a Server-usage in general and particularly a FileShareServer.
• using an over 12 year old OS like XP! (no comment further because using XP nowerdays should be a criminal ofense of neglicance usage of a PC in my opinion!)
• using many different OS accross your network is realy painful to work with. Also if you find a Vista floating around in your network you will need many new curse-words for articulating your anger with.

I think you should look into the posibility to dedicate one PC as a Server and setting up an ActiveDirectory-Domain. Makes many networking things much more easier. Once a PC is joined to an AD-Domain every settings you make in the group-policies gets replicated to every PC. Alone the task of keeping all your systems updated gets very easy to do in an AD-Domain. Setup a WSUS-Server and a few Windows-Update-Group-Policies and your server downloads once an update and all your systems get there updates from your WSUS-Server. User-logins and -data gets syncronised on all of your Systems.

Since Widows 8 you have also the hypervisor Hyper-V which you can activate and virtulize (almost) any OS you want. With Hyper-V you can easyly play around with a Windows Server.

Another cool feature of the Windows 8 era you want to look into is StorageSpaces. With it you don't have to bother with small HDDs you have flying around. Only plug it in and StorageSpaces uses it space on every (virtual) drive without beeing limited to it's capacity only.

 

From Programs and Features, maybe enable that SAMBA/CIFS 1.0 legacy option (not sure on the exact name)? Not too sure if this is specific only for 8.1, or if it also applies to 8 too.