You're looking at a different part of the site than you need to be. I just re-downloaded Xcode 1.5 for free. It's a big download because it's all of the Xcode tools as a disk image, but it is free--no fees or membership required.
When I log into ADC, I choose "Download Software" in the left hand pane, then choose "Developer Tools" and near the middle of the page is "Xcode Tools v1.5"
On the other hand, if you choose "Purchase" from the left hand pane, and then choose "Developer Tools" you'll see the $20 version of Xcode. You want the free one ;)