I have now installed RC1 (7100) 3 times.
once on a laptop took it about 2 hours but it finally finished.
Next time was on my desktop. I must have picked up the wrong Version of disc as I ended up with 7057 but that was on top of Vista I elected to new install and saved the old version as windows.old. Now this took about 6 hours to complete, but I put that down to my mirror raid was also rebuilding itself.
When it finally finished in the morning I was shall I say annoyed as it ended up as 7057 and I thought I had used my RC1 dvd, however I did elect to go online and check for updates, so whether the update thought it 7057 was better I have no idea.
Resolution says I! put my vista discs back in make sure all raid rebuilds finished then swicth to the W7 discs.
OK off we go again, download from Microsoft my RC1 again cut it to DVD.
Rename windows.old to windwosvista.old let windows 7 install again replacing w7 (7057) but do NOT go online to to check for updates.
When I left this morning for work It had been running for 1.5 hours so will be interested to see if it has finally got down to asking me for the Key by the time I go home 7 hours later.
The laptop I am using now runs well on W7 very happy with the performance.
I'll keep you posted and if there is a log I can find will tell you how long it took. I am hoping the long install is just down to the very large and complexe hardware I have.