I'm thinking of connecting a Sun keyboard to a PC (preferably via USB). Doing research I found that the most recent keyboards appear to be the Type 6 and Type 7 keyboards. What is the difference between them?
I have both. From a layout perspective, they are exactly the same. (I have both a Type 6 US layout, and a Type 7 US layout, I put them side by side to compose this reply and not make any mistakes).
From a design/construction, there are subtle differences, first of all the Sun Type 6 is GREY, the type 7 is all WHITE. Second the Type 6 lower side (near your hands) ends with a curve. The Type 7 ends abruptly (more square, if you prefer).
And perhaps the most noticeable of all, the Type 7 sports a "Sun-Oracle" logo exactly in the middle (above F8) while the Type 6 had the traditional Sun Microsystems logo at the top-right corner.
The icing on the cake for the Type 7 is its internal USB hub, with two USB female ports at the top, which the Type 6 lacked.