can Windows 7 clone the OS HDD to new SSD?
i.e have a new SSD to introduce for the main OS in my windows 7 PC, and it is of a different size to my existing HDD...
As long as the size of your current actual data is less than the size of the new SSD, and your cloning software lets you resize (most do, even downsize), you will have no problems. If not, you can use a partition manager software to downsize first, then clone it.
No, you will need third-party tools.
I would suggest the bootable CD or USB stick "Parted Magic". Do your cloning "offline" when Windows is not running from the boot CD and then exchange drives before booting Windows again.
There are other free tools, too, like XXclone and Easeus.
DO NOT BOOT WINDOWS until you have the new drive connected the same way the old one was so that drive letters do not become an issue.