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Yes, sir. In fact, I would say that is a key benefit of a CMS.
You can give different users various levels of access so that they can edit material.
Likewise, if you have a product catalog that is continually updated, you can use a catalog or store module to keep existing product profiles available... or you could use WFSections if you don't find a store or catalog module you like.
Yes, you can carry your design over to Xoops. You can even edit your theme in Dreamweaver. Also, if you have a lot of static pages that you just want to carry into your XOOPS layout, you can use something like Tinycontent or Freecontent, which allows you to do that easily.
This should help:
http://wiki.xoops.org/wakka.php?wakka=ThemeHowToAlso, if you search for "Dreamweaver" in the site search engine, you may find additional help.
A couple differences you will find. XOOPS uses CSS for colors and font sizes (which is not to say that your theme can't hard code them in the page... just that ultimately you may want to move to CSS, which helps you create cleaner xhtml anyways.
Anyways, I hope that gets you started. As you come up with new questions, first use the search engine to see what you can find. You may also find help in the XOOPS Documentation menu on the left. (This may provide help to your other users, as well, when you train them). And, as always, if you don't see it in the Docs, or a search finds nothing, XOOPS has a very helpful community... so ask and we will try to help.
Welcome to Xoops.