I can't seem to find the thread now... but there was other DLC people could download which had different pieces of armour/clothes as well as a merchant NPC. I downloaded these manually, but when I patch them into the game, they don't pop up in my inventory.
Do these only appear if I start a new game?

I believe that not all the items are added to your inventory from the starts, depends on where you are i think.
Does the Merchant show up?

In my experience, they should show up in your inventory first save you load after installing them.

Also, it's only a pair of pants, gloves, and armor that are added, so maybe you were looking for entire sets.

Nope, I knew what I was looking for, they do not appear anywhere.

Herbalist Gloves
Magician's Pants
and Roche's Vest (or something like that)

And the Swordsman Suit is actually oils and stones.

If those things are not there, double check your CookedPC folder. All the DLC files end in .dlc.

They are all going to be included in the patch today, too. So maybe that will sort it for ya.

Hope things end up working for you, TC ^_^

Will do, thanks! Its not a big deal for me really, it would just be cool to check out what theyre all about, but Im not going to cry about not having them. Thanks for your time!

Good news, then. Tomorrow they're releasing patch 1.2, which will include all of the preorder DLC for free :)

Source: http://en.thewitcher.com/patch1-2/

Wow! Just by reading about what the new patch has to offer, it seems to address all the small issues I had with the game, awesome!

Ok, so they finally showed up, I see them in the Downloadable Content option in the launcher. However whenever I try downloading them, it says connection refused. Where do I find my preorder redemption code so I can download them?

Are you trying to individually download the preorder DLC through the launcher? Installing patch 1.2 automatically installs that DLC, so it's not necessary to download them separately.