I'm going to go the other way on this. The PF1800 can scan the full density range of a negative very nicely. Your cat's image does not have blown highlights. The scanner is successfully reading the entire density range of the negative. For negatives, the PF1800 can give nice results within the limits of its resolution, which are actually quite a bit higher than what a drug store scan will give you.
Play with that focusing spacer made from an empty slide. Cut the edges so the negative itself is not crimped when the slide is closed onto it. I think on my own empty slide I had to use tape to make a hinge out of it. Once that was done, the focus of the negatives was quite a bit improved.
As for the cat image itself, it looks quite nice on an sRGB monitor as far as highlights and shadows. It does not blow out to a solid 255 in the highlights. There may be some noise in the shadows, but that isn't really the complaint, though.
If the software is locking up, you may want to look for new software. Look for 'vuescan' on the Internet. It may support this scanner by now. You can also try unplugging other USB gadgets while using the scanner.
Cat fur may be a good test of scanners and digital cameras. The fine details of sharp edges at strange angles can cause interesting digital artifacts to appear.
Brian
