How can I Get the Zen Cart Version Using a Script?

[kuroi]

There is a big chunk missing from your question. If somebody is visiting your website, you wouldn't be able to see what e-commerce packages they may or may not be running elsewhere.

So presumably you must be asking them something about their site, so why not just ask then which package they're using and which version?

Or are you suggesting that they would need to install your script on their server, indeed within their site, in order to be able to use your site effectively? If so, then for Zen cart the information you are looking for would be contained in the project_version table. I don't know for sure whether osCommerce has a similar table, though it seems likely.