I have found conflicting answers to this, so I will post it in a forum that specializes in the worst scenarios. If, for whatever reason, a user needed to use XP Pro 3’s System Restore, would .docx, .doc, .txt files be saved with it? If so, where should I save backup copies of those word files for safekeeping? If not, is there a program that is available that can restore selected files? I know I could get a flashdrive too, but I am looking for all other options as well.
System restore doesn’t destroy your documents because it doesn’t overwrite them. However, if you’ve deleted them,
restoring to a previous time will not bring them back.
The following link should help you understand exactly how System Restore works:
http://mysharedfiles.no-ip.org/TipsTricksFreeware/UnderstandingSystemRestore.pdf
Hope that helps. 
System restore isn’t a general back-up function and the files you mention are bog standard data files which I would say won’t be covered by system restore.
Any data files need to be backed up, anything you don’t want to lose should be backed up.
There are many backup solutions out there many free, so I suggest you try your friend google.
I would suggest you also look disk imaging software. I use Drive Image 7.1, the last version by PowerQuest before it was bought by Symantec and merged into its Norton Ghost disk imaging software, another option id Acronis true Image, there are others, most of them are paid options.
I take an image back-up of my primary hard disk partitions every week as part of my system maintenance. This is saved to my second HDD or it can also be written to a DVD. I also back-up volatile data files, .doc, .xls, etc. along with emails, bookmarks, address book, registration keys, etc. (anything you don’t want to lose) every day sometimes several times a day.
So if I experience a problem like yours (haven’t to date) then I just restore my last back-up disk image (takes about 15 minutes) followed by the last daily data back-up (takes seconds rather than minutes) and I will have lost virtually nothing.
Compare that with the experience of having to start from square one and the money I paid for my disk imaging software would have paid for itself if it had to be used just once if you valued your time at just £5 per hour. I have had to use it several times (not virus related) where it has hauled my a** out of the fire, it is an absolute god send.