IE5? For real? IE6 was release in 2001, which means it has existed for half the lifetime of the web.It truly does seem excessive to support IE5.
IE5 had a whooping 0.03% market share last time I saw statistics for it. Far more than I had expected to be sure, but still most likely non-consequential. How much money are you willing to spend on making this work? How much degradation in look, feel and usability is acceptable for modern browser users to support these 0.03%?
You should probably ask yourself the same thing for IE6, even though it has reported market share of 10-20%.
http://googleenterprise.blogspot.com/2010/01/modern-browsers-for-modern-applications.html
Google wrote:
Many other companies have already stopped supporting older browsers like Internet Explorer 6.0 as well as browsers that are not supported by their own manufacturers. We’re also going to begin phasing out our support, starting with Google Docs and Google Sites. As a result you may find that from March 1 key functionality within these products -- as well as new Docs and Sites features -- won’t work properly in older browsers.
And over the course of 2010, gmail and gcal will be phased out as well according to http://www.chromefans.org/chrome-news/google-to-stop-supporting-old-browser-internet-explorer-6.htm.
Have you tried a regular web search? A "css browser test" (without quotes) search gave me at least two valid sites: www.crossbrowsertesting.com and browsershots.org.