Can I transfer iPhone text messages to my pc for storage?

I'd rather do it without installing any programs if possible.

They're automatically backed up when you sync to iTunes.

You can't do it directly without third party software. Although iTunes can back up all your data including text messages it does not give access to those messages via PC. What you can do is forward them all to your email and save them that way. Unfortunately this method is tedious because it requires individually selecting each message. If you want to do this, go to a group of messages, press edit, select the messages you want and then press forward. Enter an email address instead of phone number in the "To" field.

Yes, you can do it without any third-party program. You just need to sync them to the iTunes.
But this way may be a little tedious. Here is an easy way with a reliable software program, named iStonsoft iPhone backup software.