Suppose I have a website hosted at the url:
Say this is hosted by hosting provider "A".
Now, I want to host a subdirectory within this site at another host:
...say I host this with hosting provider "B". So all the pages under this site would be at a completely different data center.
Is this configuration possible?
If you can configure a reverse proxy... then yes.
IIS reverse proxy <= is is a codeproject solution and may not have support. You can probably find many more if you just search for reverse proxy.
If you are using IIS7 (Vista, Windows 7, Server 2008) you may use the HTTP Redirect feature that is built in.