Of course, after booting up the Mac, Boot Camp complained that it could not continue and made some remark about there needing to be a single partition on this drive. Er, I did that already? Using the copy of Disk Utility that shipped with Leopard? So what's going wrong?
As luck would have it, Apple wrote Disk Utility to use the Apple Partition Map partition scheme by default default in Leopard - which is fine if you're on a PowerPC-based Mac, but hey, I'm on an Intel Mac, so now I have to reformat the drive again, this time using the GUID partition scheme. It'll only take another three hours... grrrr...
What's really frustrating is that the Boot Camp error message is so vague as to be totally unhelpful. If I hadn't coincidentally read an unrelated tech note on Time Machine not working with MBR partitions, I wouldn't have been able to solve the problem so quickly.