I don't think BE 2.5 will work with VS 2008. But, you may give it a try.
BE 2.5 is based on asp.net 4.0 and works easily with VS 2010. You can even get teh VS 2010 web developer express (FREE) version and work on BE 2.5 code.
I would recommend using BE 2.0 for your specific requirement of running blog as a part of parent website. BE 2.5 has some issues integrating with existing website. I have tested BE 2.5 thoroughly for same set up and could not get it running as a child of
parent website. I created following threads for the issue but could not get any response:
BE 2.0 works like a charm inside a parent web site. I have also created a detailed tutorial on how to integrate BE 2.0 with exisiting website.
You can check it out here:
I hope this answers your question.
Let me know if you need more information.