You need either dropboxify (the app), from what I can tell looks like the HD app has been pulled, looking at post count and join date, you probably don't have a legit way to get the non-hd version.
Or you can try gemini file manager that has been said to have dropbox support (I have not used it so I can not tell you what the level of support is). supposed to be a good file manager for a few bux.
Can't recall if Jason is adding any cloud support to Internalz HD.
Your problem lies in trying to use the web browser, it has nothing to do with TouchPad support which is probably what is confusing us on being able to fully assist you. When you kept saying you were using the dropbox app, I assumed that meant you had the app, not using the browser.
I have downloaded from both my TouchPad and Pre3 using the app today.