Welcome to the HTPC world.
Windows 7 Media Center is excellent for for HTPC use. I don't know what reviews you've read but Win7 Home Premium is the most robust, well-integrated, 3rd party supported media software out there.
Your build looks excellent with the exception of the motherboard. The 760G chipset will not offload the blu-ray decoding. Get a 785G chipset instead. If you do go for a 785G chipset, keep in mind that there are DDR3 and DDR2 boards so change your RAM accordingly if needed.
You could bump up the 240 Regor to the 245 since it's only $6 more (or the 250 for that matter since it's only $16 more). The 240 will do just fine in an HTPC however.
Also, you will need blu-ray playback software as the PowerDVD 8 that comes with your selected BD drive only outputs 2-channel audio according to newegg reviews. That being the case, you can get the OEM version of that same drive and put the money saved towards software. I personally recommend Arcsoft Total Media Theatre 3 Platinum for blu-ray since it integrates very well with Windows Media Center.