It's an opensource software. I run it on a Mac, but there is likely a PC version on SourceForge.
Software is called Huggin if I remember correctly. There is a plugging you want to get to improve the stitching. It came with image I downloaded from SF, but was a seperate manual install. I forget the name.
Takes a tad to get used to, but works amazingly well.
The "floor" post I have...the underground photo is 7 images stitched. the one above is 12 images shot with a 100mm MACRO lens....just imaging the full image resolution

It's quite amazing!