domain on a sub folder

[#1]

So here's what I'm looking to do.
I want to set up a domain, let's call it example.co.uk, and have it applied to mywebspace.plus.com/folder, rather than the main webspace.plus.com. I don't know if this is possible, or if it is, whether I can do this to other subfolders too. I'm quite happy just to use the rest of mywebspace.plus.com as I have been without adding any further domains.
Does this make sense? Can I set it up this way? How would I go about setting it up?

[#2]

Hi esseff,
If you go into your account and select Domain Names in the left hand menu, you can select configure under the domain in question then type the folder name in that you want it to point to. You'll have to have the domain registered with us to do this.
Jojo

[#3]

Hi Joanne
Thanks for that.
As I already have a domain name I'd like to use for this, can't I just transfer it in and choose the folder? What's the difference between transferring and registering?

[#4]

As far as I'm aware the domain needs to be hosted at Plusnet but needn't be registered there. The 2-step transfer process is explained in the Hosting Only section of the Hosting guide.
David