Should you reinstall XP without SP3? NO If the only problem with Windows is OE.
When some people install SP3, they reboot and discover problems. Once the problems are fixed, SP3 is unlikely to cause further problems as it's the installation process that seems to mess things up, rather than an ongoing conflict.
Besides, it's only a suspect and because OE is now working in Keith and a similar problem is developing in Jocelyne, while the guilt isn't proven, the CA AV is moving up on the list.
It might be simpler to go back to ONE  account for the computer but I need to have two  seperate email addresses working and file emails into two  sets of folders in the same OE6 screen. Is this possible?
YES. It's even simple to do. Each OE Identity can have multiple E-mail Accounts
Going back to a single User Account is up to you but not necessary for having two mail accounts in the same OE Identity.
You can can even do it in both User Accounts if you like, or in one or the other. The OE Identities are independent of each other so you can have the same E-mail accounts set up in different Identities.
Now to what's going on with OE. You have a problem with the Identities in OE, not to be confused with the Windows User Accounts.
I'm betting from what's happening it's a corrupt DBX file or two, but it could also be in the Registry keys.
The Identity that was accessed through the Keith Account started off with a severe corruption that wouldn't allow the program to open. By accessing the program in a different way, OE managed to create a new file(s) or Reg key to replace the corrupt one(s) and enabled it to start working.
The Identity that is accessed through the Jocelyn Account either had a mild corruption that enabled it to work for a while and now it's getting worse, or it started out OK and is developing corruption (this is where the AV would move up on the suspect list a bit more).
If you want to leave the User Accounts and OE Identities as they are and fix the Jocelyn Identity, then give the following a try.
From your descriptions of what happens, I'm strongly suspecting a corrupt Inbox.dbx.
To check if that's all it is, log into the Jocelyn Account.
If it starts. click Tools>Options>General tab.
Uncheck "When starting, go directly to my Inbox" and also uncheck "Send and Recieve messages at Startup". Click Apply.
Click the Maintenance tab>Store folder button and find the location of the Message Store for this Identity.
Click Cancel to return to the Options and then click OK.
Close OE and navigate to the Message Store folder for the Jocelyn Identity and make a quick backup of it like you did for the Keith Identity.
If it's a corrupt Inbox.dbx, you should be able to access OE normally in either User Account. The program should load fine and let you use the tools and menus.
Give it a try and see if it works consistently.
If you open the Inbox to view messages or try to receive mail, it may freeze as it's been doing. If it does, but works fine until you try doing one of those, if you manage to get the Inbox open, move any messages you want into a new folder in OE of your own creation.
Then go into the Jocelyn Message Store and delete the Inbox.dbx.
Try OE again (switching between User Accounts as you've been doing) and see if the problem persists.
If it does, the next thing to try would be to create a New Identity in OE. That will create all new DBX files and Reg keys.