If the old disk was cloned to the new one (seems unlikely if your image is 250 GB) nobody it's totally transparent for everything you can imagine, even before you erased all evidence by overwriting it with the first 80GB of your image.
Only if they did a clean install on that 80GB (and didn't change the BIOS date before doing that) and the disk wouldn't have been overwritten, you could have seen the creation date of, say, the Windows folder.
I would like to know that is there any method to diagnose the HW change of a laptop. Does the bios store any log about that? We have laptops in our university that are borrowed by students. Recently we found that the harddisk of one laptop was changed from 320 to 80 GB. We found it when we tried to install our custom OS image (250GB), but it deletes all previous OSes, including boot record. We don't know who did it, but if we can find when the HDD was changed (the date), then it is possible to find who did the crime. Thank you.