I'm not finding a question in your last two posts. I suspect that you want to know why KDE isn't installed and loading. I don't know, all I can say is that it certainly loads and installs for me. You say that you chose the desktop environment setting, but that's all I know about your install (other than you are trying to dual boot with MS), so I couldn't even go back and try to duplicate your install if I had the time.

I have installed Debian both in dual boot and stand alone systems without seeing this problem. When I do a dual boot I do not personally choose to let the Linux boot loader install to the MBR, I make it install on the Linux partition and then use XOSL or SBM to boot whichever system I want, but I know of no reason why you would have problems installing the Linux boot loader to the MBR. Heck, I use XOSL even with Linux only, I just find it keeps my options open and saves me from fooling with grub or lilo issues.

You may need to wait until someone with more Debian experience than I comes across this post and can spot what you are doing. I expect that Underscore will know what has gone wrong in your install, and that there must be a few others here who will catch it too. But even they may need a bit more feedback than just that you chose the desktop install.