I have searched but can't find a simple answer!

I have my pop accounts set up to forward to my BB account. Can I now set up my desktop to retrieve the BB email via outlook express?

No.

I was hoping to do the same thing...

Currently impossible.

According to this link BlackBerry Internet Service v2.2 Release Notes soon you will be able to auto-forward emails from BB to another account. You can use Outlook to retrieve forwarded BB emails from that another account.

What you need to do for the time being is to have mail running through a third party email account and then either forwarded to or integrated with BIS. You can then always pull mail from that third party account directly.

If you have mail going directly to the *.blackberry.net email address you really shouldn't as you're up a creek without a paddle (well, aside from burning the boat and creating an entirely new *.blackberry.net address) once you start getting spam to that address.