I'd expect any monitor or video card labeled "HD" to also support HDCP over DVI, which older hardware doesn't. And you'd need that to play Bluray content.
I agree but some videocards have HDMI outputs which will connect directly to an HDTV or an HD monitor with HDMI imputs.
other monitor inputs are dependent on your videocard.
If you have a Blu ray player in your computer it will certainly display Blu ray movies, otherwise why would they put it in your computer?
a computer has a BD-ROM drive. It happens to be able to also play BD-Video.
With the ability to add firmware updates to a standalone BR player I'd suggest saving up for one that has BD-Live Profile 2.0 as you can get a lot more content via the Internet and have less issues with new discs that have newer DRM software.
If you are purchasing a new computer monitor consider getting one with HDMI inputs.