Ok this might be a dumb one - but bear with me.

I have bought a domain name (A). I have a hosting service that I have bought from digitalspace (B). A points to B, works great.

Now B has a lot of space that I want to use for other domain names (both bought and free sub domains)

Now how do I get a free subdomain (say helpme.110mb.com) to point to "my" digitalspace server?

I am lost, not sure if it can be done, and if yes, how?

Either use a portal page with links to both sites or your host will need to provide 2 different ip addresses, one for each domain name.