Since it's a 1G iPod Touch, the latest OS it can hold is version 3.1. See this article for information on how to update to this version.
http://support.apple.com/kb/HT2052
I am having the same problem...However, when I click on the article's link, it brings me to the iTunes software download page. I really would like to get v3 for my ipod.
I have the same problem (want to download 3.1.3 but I get re-directed to the Itunes download page), have tried different browsers (explorer, chrome, opera). Does anyone know what should be changed in order to not get re-directed?