It varies somewhat by which set files you've installed, but there's not really any way you could squeeze Complete into the internal memory of an E2. You'd have no trouble with Basic, though, and even the Professional version should work as long as you limit yourself to the bare minimum of font files and install the handwriting recognition data files manually instead of using a keyfile.
Practically speaking, though, SD cards are so cheap (I've seen 64MB ones for under $10 in some places) that even if you can squeeze PlecoDict into internal memory you're probably better off just getting a card - it'll leave you room to grow later if you want to add on any new dictionaries (either the free ones or the new paid ones we'll be introducing in a few months), and it'll help ensure that you won't be left out if we release an update with audio pronunciation or stroke order diagrams or some other data-file-intensive new feature.