The New Poser forum was created because more experienced Poser users would jump on the new users when they asked a question.

Im sorry to say it, but that is not a valid reason i think. If experienced users are jumping at people asking basic question then there is a problem with your users. Also experience is a grade, even those that see them self as experienced, might be "noobs" in the eyes of someone more experienced, so what prevent those at having a go on them?

And you can keep asking that question, so if that is such a huge problem that you have to make "special" forums for people, you really have to sort this out, i think. Besides that you could make a sticky or a beginners guide, where all the most basic questions are collected and answered. Like:

How do i make cloth follow my figure?

How do i setup a dynamic cloth simulation in Poser?

And you either make a link to these beginners guide when a user register, which is a good service and give them a good experience straight away or you could do both. Also the more experienced users could refer to this guide rather than having a go at them.

We have vendors that use the Marketplace Showcase forum for displaying products that are coming out soon so since it is getting used, it would not be good to take it away from them.

I see your point, but i have to disagree. Looking at the forum there are 2 posts and the last one is made the 29 january announcing the release of a product, meaning that its already available on the marketplace. Besides that it have 7 views. The other one is made the 18. jan and have 13 views. I like that you don't want to remove that option from vendors, but i would say that the numbers speaks for them self how effective or useful this is, both in regards to the users and the vendors. When comparing to reducing amount of forums, i would get rid of it. The main way for vendors to show or promote there products are through the product page, so if you want vendors to have better options for presenting them and viewers to get information about them, this is the place to do it, i think.