If it's a HP Scanner 3500c, it's compatible according to this
http://testedproducts.windowsmarketp...2-0566c95da701

If it's a HP Scanjet 3500c, it's compatible according to this
http://testedproducts.windowsmarketp...c-7d3d559e0901

If it's a HP Photosmart 3500 scanner, it's not compatible. The 3600 is, but not the 3500.

And if it's a HP Laserjet 3500, it's not compatible.

So, I'm going to continue to look based on the fact that it's either the first or second items listed here that are compatible.