Reinstalled Windows to a new SSD and reinstalled Xtreme, however, it has reverted back to the default profile. I have the old disks so should have access to old data and I was hoping there is a way to copy the old profile over to the new SSD so I don't have to rebuild everything.

Winstep applications store their data in the Windows Registry.

So, unless you made a backup of your settings before switching over, I'm afraid you are out of luck.

Unless you know a way to access the old Windows registry database (it might be possible, but, if it is, I don't know how).

And that could cause even more problems. Thanks

Actually, you can. I don't remember where Winstep stores its data in the registry, but each major registry branch has its own file where it's stored. Now, if you know it's, for instance, HKLM (HKey Local Machine), you can locate the old registry's file within Windows (i.e. C:\Windows\somewhere\blah\).
After that, you can go to RegEdit and do a "Load Hive", point it to the old file, give it a nice distinctive name so that you know which is which, and then navigate to the proper branch within it and export the data you need.
After that, unload hive, edit the .reg file you just exported so that its identifiers point to the main registry (instead of the loaded) and... well, you know how it goes after that.