Having somewhat of the same problem, I have basemaps to choose from in the menu but nothing loads. I get a blank screen no matter what map i want to look at. Had the same problem with 1200 but 900 worked fine.
Is there a solution to this problem? If ArcGIS Explorer gets the basemaps from a URL address does this mean that it checks this at startup and if you are behind a proxy this becomes a problem?
I seem to be having the same problem as Adam, with the basemaps not loading. I've tried it on a few different PC setups, and noticed that it seems to work fine on WinXP and Win7 32bit PCs, but not on WinXP 64bit. I was wondering what you guys are running AGX1500 on?
Found my solution. I'm running dual monitors, and Express needs to run on the main display on my machine/video card. ArcMap will run on either, so not real obvious ...