Here's the background for anyone who has forgotten:(Courtesy UESP Wiki)

When you first get to Bleaker's Way, you need to find the fake evidence. Inside Nivan Dalvilu's house you will find a Dalvilu Cermonial Dagger [sic], located on a low table to the right of the entrance; this dagger should be planted on Hrol Ulfgar's body after you've killed him. In Hrol Ulfgar's house you will find the Ulfgar Family Ring, located next to a Guide to Leyawiin on a table near the base of the attic stairs; the ring should be planted on Nivan Dalvilu's body also after you've killed him. Wait in their houses until they come home, and kill them. Plant the evidence listed above.

I've done all that except for the planting part. What actions do I take -- I'm on a PC -- click e? just drop the item? what? I've tried everything I can think of but i'm not getting it done.

I know it's got to be simple, but what?

You have to leave the items on their corpses. Just activate the corpse and then place them in.

I'm not quite clear about that. What are the keystrokes? How do you mean "activate the corpse"? And how "place them in"? Sorry to be so obtuse but I've been trying to do that over and over.

The process for switching between giving and taking items to/from corpses is the same as switching between the buying and selling windows when talking to vendors. Planting the evidence is basically you selling the evidence to the correct corpse, if that anology helps.

It is the same as when you loot the body of an npc you just killed. The corpse acts as a container, the same as a chest would. Simply do the same things you would to move an item from your inventory into a chest.