You can purchase the iOS 3.1 Software Update for iPod touch (1st generation) from the iTunes Store using the latest version of iTunes on a Mac or PC. 
Purchase the iOS 3.1 Software Update directly from the iTunes Store.
Own an iPod touch (2nd generation or 3rd generation)? Get the free iOS 4 Software Update for iPod touch.
If [...]

Immediately after updating to iOS 4, some users may notice that Exchange ActiveSync Mail, Contacts, or Calendars do not sync, or sync very slowly. In addition, some Exchange Server administrators may notice their servers running slowly.

On iPhone, iPad, and iPod touch, you can save images from a variety of applications (such as Safari, and Mail) to your device. With your iPhone, you can also capture photos using the built-in camera and video footage* with the iPhone 3GS and iPhone 4. The following document will help explain how to import this [...]

If you are having issues with an iPhone, iPad, or iPod touch accessory, try the following troubleshooting steps:

iOS 4 devices are unable to resolve unicast DNS names that end with a “.local” suffix, affecting access to internal corporate networks that use an internal, top-level domain name, such as “mydomain.local”.

Learn how to reset or restart iPod following a freeze.

Remote is a software application for iPhone and iPod touch that allows you to control audio and video playback in your iTunes library and on Apple TV. This article provides resources that explain how to setup Remote and troubleshooting issues that may arise. 

In Windows XP, some background processes can cause issues that may prevent applications such as iTunes and QuickTime Player from working correctly, opening, or even installing. Learn how you might resolve these conflicts by disabling some items using the System Configuration Utility (MSCONFIG).

Microsoft Entourage 2004 and Microsoft Entourage 2008 are Mac applications with which you can sync contacts and calendars with iPhone, iPad, and iPod touch. 

iOS 4 Software Update is a free update offering new features for iPod touch (2nd and 3rd generations). Features and capabilities vary between iPod touch models, with some features available only on newer models.