According to a posting on Microsoft's Swedish partner blog we could be seeing the Windows 7 release candidate in early April. The blog also hints at a RTM and business launch of Q3 2009. According to the blog Michael Bohlin, a Windows product manager, was questioned over Windows 7 availability. The blogger also states "the cut of all internal guesses here in the office right now is October 3 at 11.10" for the RTM date. Windows chief Steven Sinofsky posted a blog entry today to put to rest any rumours of a beta 2 for Windows 7 and confirm the next release will be the near final release candidate. Microsoft is currently rumoured to be readying an interim build for Windows 7 testers for next month. source: neowin.net
I highly doubt that it will cook as long as October before going RTM. I anticipate July or early August for RTM. Though they might let it go that long but if they are looking to deliver the first RC in April then your looking at least another 1 or 2 RC builds and maybe an Escrow build if October is the target RTM date.