downloading text messages from iPhone 3G to windows laptop XP professional?

The easiest way is with 3rd party software, such as MobileSyncBrowser. Else, you can take screenshots of the messages (quick, simultaneous press of the home and sleep/wake buttons puts a screenshot into your Camera Roll) and email those screenshots to yourself, one at a time.

As i know sms and contact stored on DB files, which files and is it possible to copy them to desktop for backup then return them back when ever crash or after clean install to my iPhone3G 2.2?

The native backup solution for the iPhone includes backing up of text messages. By trying to change the the backup files (adding in older files, changing the data within a current file, etc) you may end up corrupting the backup rendering it useless.

But if all he wanted to do was download, as the OP mentioned, you still need to find a specification of the structure of the db files in the backup.

AFIK Apple has not released that.

Google might help.

But the OP also mention restoring them to the iPhone in case the phone crashed. I probably just such a corporate IT shill, that I don't recomend that people makes changes to files without haveing thorough documentation and experience making such changes.

icebike wrote:
But if all he wanted to do was download...

...then s/he should click on the link in my post above!

No, it is not. In fact, prior to MobileSyncBrowser, the only way to access the data was to manually parse the SQLite database files using a command line script and some intuition, which is what icebike was referring to above.

I should point out that MobileSyncBrowser is not accessing the messages +on the iPhone+, but is actually mining the data in the iPhone backup file on your hard disk (that's how the manual method works, too). That means two things - 1) it works without the iPhone attached, and more importantly, 2) to get your SMS messages, you'll need to have synced your iPhone to allow the backup to be made, so it's current.