You'll need the 19 Mb package either way. The Desire HD will probably be able to cope with the HD pack, but if you run into any graphical glitches the HD pack is easily uninstalled so you can revert to standard.
On a similar note, we're in the Market 10 cent sale once more, which means our download servers are being hammered once more. If any of you receive an "incorrect file size" error, the file is fine, it's actually a connection error. Keep trying and you should be able to get through.