Actually, that is incorrect - unless you have previously purchased SlingPlayer for iPad, it is unavailable for the iPad 1. The current version of SlingPlayer for iPad requires iOS 7, and the iPad 1 is limited to iOS 6 (or lower).
However, you may run SlingPlayer for iPhone on the iPad in Compatibility Mode - it actually looks great, even though it is 2x larger. But again, unless you have previously purchased SlingPlayer, you're unable to run it on an iPad 1 - minimum iOS for SlingPlayer for iPhone is iOS 6.1. (highest available on iPad 1 is iOS 5.1.1)
Please see the footnote here for more info on iPad compatibility:
Is there an answer to this last question? I just bought a new PRO-HD and everything I read prior to purchase (e.g. http://uk.slingbox.com/go/spm) indicated that my iPad1 could be used. However I now come to trying to install the Slingplayer App and neither version says it will work on the iPad1 meaning I have no way to access my Slingbox!! HELP!!