Have you tried Software Update? I just had an interesting experience. I had just checked Software Update and knew my software was up to date. Then I plugged in my HP officejet d135 and added it as a printer and checked Software Update again, and found a HP Driver upgrade of some sort. Evidently some sort of a generic one, which I downloaded. To my astonishment, the d135 started acting like it would print. The icon that came up was a generic printer icon and NOT the d135 icon, but for the first time since going to Snow Leopard, I had a response from this printer.
In reality, I don't think the d135, which is 8 years old, has a snowball's chance of being compatible with Snow Leopard, since it theoretically is only compatible with 10.4. But it had worked in Leopard, and I was curious enough to see to see if it would work in Snow Leopard. It doesn't really--it thinks it's printing, but just sits there thinking it's printed 8% of the document. But I was surprised at even that much happening.
No idea whether or not the generic driver from Software Update would work on your HP PSC 1400 or not, but maybe worth a try.
Good luck!