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Personally, I would leave the existing infrastructure in place. Itís an open source platform with tons of information available. Youíll probably spend less time getting a handle on PostNuke than you will migrating the entire site to a new platform.
Would it be better for a website to not have any CMS at all?
That would depend on the purpose of the site - but for the most part - probably not. You said it's your company's site, right? If you're changing content on a regular basis a CMS is the way to go.
I think that's why they call it a content management system ;)
Perhaps you just don't have the right CMS for the job. Dreamcatcher's resource above seems to be pretty good for nailing down which tool is best for your needs/site.
You have to consider growth. With a good CMS, if you decide you want a newsletter, the solution is already there. If you want tagging of articles, the option is available to you. E-commerce? Forum? Spam prevention? It's there. Etc.
[drupal.org...] rocks the house!
The open source cms website offers free demos, but be aware that these are the base installations. Go to the project homepage to see what else is available in terms of add-on modules.