Quote - 1) I'm using V4 with skins and morphs, blah, blah, blah. I bought a few nice character outfits -- more than I can afford. I still have a lot of problems with poke through. I use the morphs to try and adjust, but it's often a tedious process with fairly mediocre results. Is that just the way it goes, or am I missing some important trick of the trade?

First off, make sure the clothes are indeed Fit To the character -- not all items will auto-conform.  Are you getting poke-through because of the morphs you're applying to V4, or the pose?  Clothing items don't necessarily have all of the morphs, so they don't respond to all morphs.  There are several solutions:
--You can use a utility like Morphing Clothes, Crossdresser, or Wardrobe Wizard to add the morphs you need
--You can check which morphs are included in the clothing and try to achieve the character you want without using morphs that aren't in the clothing
--You can make body parts invisible if they wouldn't be visible anyway
--You can fix it in postwork

Quote - 2) When I render, there often appears to be a painterly quality to the images, as if I'm seeing vague brushstrokes. Any tips on making that less obvious or is it just lighting?

Can you post an example of what you mean, and your render settings?

Quote - 3) Right now, I'm using only D/S. It seems to be the consensus of many that the most photorealistic renders need a lot of postwork. I have access to an old version of Photoshop. I also have (way more difficult to achieve) access to Poser 7. Which is the smart way to go?

It's quite possible to create photorealistic renders in D|S.  Lighting makes a lot of difference.  There are some lighting characteristics that aren't built into D|S -- many people recommend the Uberenvironment plugin.  Whether you use D|S, Poser, or Photoshop to achieve it, it's a skill that takes time and practice and learning to achieve.  I'd recommend picking the tool that you find most comfortable and learning how to get the results you want from it.  As you become more skilled in that application, you can decide if you want to learn how to supplement it with another application.  Don't assume you can't achieve what you want in D|S.

Quote - 4) Oh yeah, and to get truly newbie on you: What are shaders and what are they for?

Shaders and shader presets are essentially instructions to the rendering engine about how to render materials.  For example, there are shaders/presets designed to give a metallic appearance, or a glassy appearance.