EDIT: I also unregistered my iPhone because I bought an S4 and couldn't receive texts from those with iMessage turned on, as their phones were still iMessaging me. Am I doomed?
Looks like iTunes on XP stores backups at this path: \Documents and Settings\(username)\Application Data\Apple Computer\MobileSync\Backup\. That's the directory you need to recover from the hard drive.
I wrote an export script in Python that's fairly popular (200+ stars on Github): https://github.com/toffer/iphone-sms-backup
Unfortunately, I never did get around to exporting photos and videos.
Hopefully the bug at least only allowed someone who was a friend of a friend (she was, just not my buddy's) to appear in the wrong list. Super sketchy if it was actually rendering complete strangers!
Regardless, I'm pretty sure if it wasn't for that bug I wouldn't be married to my incredible wife :)
I'm looking forward to seeing how well it works, specifically whether it can pull photos/videos as well. If it doesn't yet but it wouldn't be too much trouble to add, I'd be willing to literally pay you to add that.
[Edit: Since a lot of the other comments are questioning the value of saving this stuff I figured I'd share my use cases. It turned out when I thought about it I have at least three:
1. I effectively met my wife on myspace (believe it or not a pretty nasty software bug led to our relationship) and an enormous amount of our initial friendship and courtship ended up documented there. Years ago I painstakingly clicked through for hours and copy-pasted the conversation to a text document.
2. I had a close friend die very suddenly and at a young age. My memory generally kind of stinks and I hated that there were conversations with him that I half-remembered. I went back through social media conversations with him (again, mostly on myspace) a lot in the years that followed. It helped me piece together memories that are very important to me now.
3. This past year my wife and I adopted our daughter. Our relationship with her birthmother has primarily been via SMS and the months that followed were a really exhausting and beautiful blur. It's really important to us that we're able to share that thread with our daughter someday.
In none of these cases did I see it coming that these services would end up having such valuable content in them for me. I didn't know I'd meet my wife. I'll never know when the last time I talk to someone is, and I would have never guessed that one of the most important things I'll have to give my daughter about her birth story is an SMS conversation.
So yeah, having access to this stuff is important to me. Thanks to jwz for pulling these resources together. ]