Since looking up the computer model doesn't seem to be leading to definitive results, how about a visual check?
charlie, I'm assuming you have the Toughbook in your possession. The hatchway to access the RAM is usually screwed onto the bottom of the case. Remove one stick of RAM, and post whatever's printed on the label back to this thread. The label will include (among other things) the manufacturer, the manufacturer's model number, the memory type (DDR, DDR2, DDR3) and the memory speed (PC-3200, PC2-5300, PC3-1066, for example).
Notice how DDR, DDR2 and DDR3 have different speed codes; the prefix (PC, PC2, PC#) tells you which type it is.
DDR, DDR2 and DDR3 also have different numbers of contact pins, and locator slots in different positions, so you can't fit a chip into a slot for a different type unless you really force it. Here's an image comparing the slot positions for the different types:
If worst comes to worst, you can always do it the old-fashioned way. Go into a local computer shop with your Toughbook, and tell the nerdy guy behind the counter: "I need RAM that will work in this laptop". They've definitely got stuff around, and since it's likely to be used, you should get it for cheap.
Since looking up the computer model doesn't seem to be leading to definitive results, how about a visual check?
charlie, I'm assuming you have the Toughbook in your possession. The hatchway to access the RAM is usually screwed onto the bottom of the case. Remove one stick of RAM, and post whatever's printed on the label back to this thread. The label will include (among other things) the manufacturer, the manufacturer's model number, the memory type (DDR, DDR2, DDR3) and the memory speed (PC-3200, PC2-5300, PC3-1066, for example).
Notice how DDR, DDR2 and DDR3 have different speed codes; the prefix (PC, PC2, PC#) tells you which type it is.
DDR, DDR2 and DDR3 also have different numbers of contact pins, and locator slots in different positions, so you can't fit a chip into a slot for a different type unless you really force it. Here's an image comparing the slot positions for the different types:
http://en.wikipedia.org/wiki/File:Laptop_SODIMM_DDR_Memory_Comparison_V2.svg