Just want to share my experiences.
1) I downloaded both versions 1.7 and 2.6 for the 64 bit from this site: RT Seven Lite - Downloads
I chose the iso option as in para 2 of the tut, but with both versions I got the error "select bootable Windows 7 os" when the app was pointed to the iso. Googled for it but couldnt get a solid fix so i extracted the iso using winrar to a folder on the hard drive and pointed the app to that. That worked fine in both versions.
2) In ver 1.7, theres no box "Slipstream service pack" as described in the tut, so I went to the task panel on the left, chose Integration and then tried to point to SP1. That was a no go because one can only choose a .msu installer and as we know the SP1 is an .exe. In any case, I switched to ver 2.6 and that let me select the SP1 as described in the tut.
3) Para 4 is the longest step, took over an hour though am on a core i7. The "Proceed" button appears only when the integration is complete. Along the way, the window may show "not responding", though the hard drive is working like crazy. Must be patient.
So now the SP1 iso is ready. Will burn dvd and post later.