The prop/background approach is an excellent one.  I forget but there is a posing tutorial which outlines step-by-step the method to accomplish this.  Of course keep in mintd shadows cast on a flat prop will yield flat shadows.  I used this technique to creat the background on my avatar.

Have you tried conforming the belt first to the character, then parenting the prop to the belt?  Or try positioning your prop to the character's hip and actually parenting it to that body part.  It may correct that problem you're having.

Agreed.  Unless the background serves a larger purpose render without it, export as png and compose your scene in Photoshop or PSP.  But to answer the question, it sounds to me that your dimension settings are off.  Check to see if the 'match the preview window' button is selected.

I agree with the majority on this problem.  Also check the resolution quality of each actor/prop in your scene.  Too many hi-res texturing can choke the system.  Lighting is really a big issue, and the fewer you rely on the better.  Maybe using an overall IBL to fill the scene is the answer.  It will illuminate everything and reduce the dependence of other light sources.  Or render in three stages, foreground, middleground and background, and then reassemble the entire scene in Photoshop or PSP by layering each render over each other.  I have successfully created renders in such a matter when I felt the system was too overwhelmed by the volume of objects in the scene.

Are you using multiple lights in your scene and are they all casting shadows?  I need some clarification to address your problem accurately.

My concern with using the method MetrixWorkz describes is the loss of resolution from lossy to lossless format.  I would agree with IsaoShi about placing a one-sided square as part of your background and then "texturing" in the material room with your background.  The other workaround is to save it as a tiff, another lossless format which preserves an intact alpha channel.

A custom light set would be better off saved in the library.  I do agree with ockham, deleting all the lights from the scene to be imported will prevent headaches later.  There is a tendency for poser to import lights along with the character multiplying the illumination beyond what you intended.

It is almost impossible to try and keep track of some many runtime folders without a structured, logical arrangement that works for you.  I tend to create runtimes for projects and load content specifically used for that project.  Once done, the runtime folder is either transferred to disk and deleted off the HD or completely deleted if certain I will never go back to it.  The most used content get their own runtime folders for easy access (i.e., Poses, Props, individual characters, Themed, etc.)

There are two alternatives to this querie, save the character into the library or save it as a pz3 and import the poser document into your new scene.  I use this method when creating individual components for a major scene without cluttering my library with content I'm only using once or twice.

I, myself, have several external runtimes sitting on my hard drive which actually make my access easier and more controlled.  It is figuring out a logical method of organizing your files without wading through one enormous runtime file.  But there is a disadvantage of too many runtimes.  I tend to break up my projects into individual runtimes; load what is necessary for the scene, compose and render.  Afterwards, the project is either burned to disk and removed from the hard drive or delete it completely if I feel I will never need it again.  This is a great Tutorial and many individuals will benefit to read it through before amassing an unmanageable runtime.  Been there, done that.

It's good that you have found something that you are comfortable using.  Many individuals give up without developing basic knowledge first; in essence giving up on a great opportunity to develop artistic skills.  Have we become a society striving for application instant gratification that we forego learning something that could become truly amazing?

Thanks for the post.  Always interested in DAZ freebies.

Quidam has released a new mesh application called Argile and, my understanding, you can custom alter head mesh for morph targeting.  There is a video tutorial demonstration on how it is done.
This is the link if you are interested pursuing this avenue:
http://www.n-sided.com/3D/argile.php?rub=1

I believe there is also a demo program in the free section here on Renderosity.

I am rather surprised that you are unable to get free content to appear in Poser considering that most free content adhere to the runtime hierarchy convention.  Of course, if you are lacking the correct model in your application then the free content would be almost completely useless.