Firstly I installed it with the VelociRaptor dangling out the side of the case, which took from 18:55 to 19:10. Then I located the redundant hard drive, which turned out to be a Maxtor 250GB. I removed that, connected up the three remaining drives (the old system drive, and 2 * 1TB), and am now starting the app install process. That's going reasonably well, and I have Office and Steam loaded, and a handful of others.
iTunes proved to be the most problematic, because for some reason the My Music folder defaulted back to the C: drive after I moved it. It took me a while to figure out where the default iTunes database was, but once I did I just copied the old database over it, and all my music appeared again in the library *phew*. Thankfully iTunes doesn't do clever things with its database.
Next on the list is reconfiguring Outlook, and that's about it.
I opted for the 64bit version in the end, and so far no problems.