One thing to be careful about Brian is that Version 6 didn't use the same backup options as the newer versions. You could do a "simple copy" which just made a copy of the user folder or you could use the Windows 95/98 backup feature. If the V6 data was backed up with the Windows backup, you may not be able to restore it using the Win XP restore command. I suggest you use the File, Backup, Simple Copy and copy it to a CD, Zip or Flash drive then just copy it back under the Peachw folder on the new PC.
Realistically, all the data is stored in the company folder located under the Peachw folder. When creating a company folder, Peachtree uses the first three letters of the first company name word, the first three letters of the second word and the first two letters of the third word. For example if the company name is Alpha Construction Inc, the data is stored in ALPCONIN.
The user should then really upgrade to a new version of Peachtree because if they have any customized forms (invoices, checks etc), they may have difficulty using them on a new operating system, especially if they have a new printer as well.