It's better to have the latest edition, though older versions are not worthless, of course, as code from a few years ago is perfectly valid now (even is not the latest available).
Be aware, however, that the code samples available for download are for version 3, so they won't match the text in version 1. We can hook you up with the files for version 1 if need be, but I'd go for something more up to date. If cost/time is an issue, you could grab the PDF version.
Somewhere in the opening pages of the SitePoint books they always give the URL for the code download, but it won't be relevant for the first book now anyhow (though it should be ... tisk tisk.)