For example a Dell Optiplex 780, with like a Core 2 Duo, SATA HDD, 2-4GB of RAM, from the release version of Windows 7 all the way up to Service Pack 1 with the latest KB.
Hours. Since Windows 7 only had one service pack, even with super-fast internet and an SSD, you are looking at a lot of CPU power needs and quite a few reboots.