WordPress on subfolder needs to point to subdomain

Hi,

I have my wordpress hosting and install on mydomain.com/blog.

I have a subdomain which ranked well for my old blogger blog blog.mydomain.com and have migrated all the content over to wordpress.

I want to have blog.mydomain.com to point to my new wordpress install in the subfolder on mydomain.com/blog and resolve as blog.mydomain.com also.

My first question is will this transfer my SEO google juice, or loose it all?

My second is that so far I have achieve blog.mydomain.com going to mydomain.com/blog, but not resolving (showing) as the subdomain. What can I do about this?

Thanks for your help ??