I deleted all the old 1.5.2 files, deactivated my plugins, uploaded all the 2.0.3 files, then used the upgrade.php page. I click the "Upgrade WordPress" link, wait patiently like I'm supposed to, then I get a blank page, except for the WordPress header at the top.
I'm stuck in a sort of limbo. My blog still works and I can still post new items, even though all my 1.5.2 files are replaced.
The problem is that I discovered that I can't post photos on blog posts. They don't appear unless I make them display from an old host. I'm scared to death to even tough my theme files, but I will have to soon.
I've deleted and uploaded three different times with the same result.