My wife's work gave her a machine with XP Pro (so she can work from home). She will keep the XP Pro machine. Her desktop at home is XP Home. Can I pull the HDD out of the XP Home machine and just pit it into the XP Pro machine so she can still use her stuff from home without having 2 PC's

Yes - with caveats.

Do you have permission to alter the company PC?
Does the 'new' machine have a free IDE or SATA port?
Do you wish to boot into your wife's XP install?

Yes - The PC from work is hers to do as she wants.
It does have a couple of open SATA's.
She wants to open in Home so everything is familiar.
The other advantage of the work machine is newer with better hardware

Do you mean boot?

This is possible, seldom easy. It is necessary to first attach the 'old' drive as a secondary drive. A simple modification on the 'new' XP drive is required. C:\boot.ini needs a new line(s) of text added.

Following that, on boot you will see two choices, basically -
Choose the "new XP" or the "old XP"

New XP will work fine. Old XP will probably BSOD and/or restart. You might get lucky and boot, and we can predict exactly how lucky, but if the new machine is at least one generation newer than the old one, that luck ain't happening.

We take it from there. Many will tell you, "Too bad, cannot be done." And they are almost right.

It will NOT be easy to support this remotely. You will need your best mind on and some degree of experience.

I forgot...

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