I just learned that VSD wont render an image larger than 2000 px... what's up with that?

I don't know if there's a technical answer or that's just what it was set to. Your not the first to ask.

That's one larger picture.

So how would I go about making a page requiring a foreground image larger than 2000px? Just hand-code the image in?

Yup.

Is it a background image (texture, pattern...) or a photograph? If it's the former, it can be repeated to fill the page so it doesn't have to be so large. For a photo, maybe it could be 'sliced' and inserted in sections? One image over 2000px wide/long could take an awfully long time to load - I don't think too many people would wait for it
Here's some info about over-sized backgrounds that might be useful:
http://www.webdesignerdepot.com/2008/11 … ckgrounds/

It's a background image, though not as a background image, if that makes sense.

Thanks for that link - I will now tile the image on the y-axis!