d-i with the 2.6 kernel is so close I can taste it. In fact, images can be built now with only one hacked udeb, and it boots up and works fine all the way to partitioning. The partitioner does not see ide devices, but this is probably something stupid, since the kernel does.
Update, 3 pm April 14th: success!
Update: 21 April: Daily built CDs can be booted with "linux26", and it installs fine. A 2.6 kernel is not yet installed, and there are a few minor problems as documented in bug #243761.