I came across this article the other day, while looking for something else.
It appears that in 2008 Jim Rowe had a problem with some I2C devices. He contacted NXP (was Phillips) and they supplied some software for testing I2C.
The March 2008 Silicon Chip article is available online(but not free) http://www.siliconchip.com.au/cms/A_110147/article.html however the software and board layouts are available to download at http://us1.webpublications.com.au/static/downloads/articles/110144_I2C_interface_sw.zip There is a small piece of hardware required to interface to the printer port. I do have a scan of the schematic, but no website to drop it on.
I haven't tried it yet, but it may help someone.