Firstly I'm quite surprised at the response you got Dave - it doesn't appear to answer your question - let me see if I can clarify this as I can see you do have a couple of issues here.
You're a webmaster of the site - meaning you have admin access only and can make changes to the site but you can't install modules - I would say that being Portal 19 indicates you're one of several sites on that build - and that's ok you know because I run many of my sites the same way.
However, it seems that you're perhaps a bit more savvy than the last webmaster and wanting to do more with the site - and that's great news - it means the company will benefit from your efforts, but it also means you may have outgrown your current method of site management.
it is a problem for the web hosting company to upgrade their portals if they have several sites running it because you don't know the implications of the other websites that are sitting there. I wrote a blog about child portals and their use - you might find it helpful to understand and how it relates to your situation because you are in fact a typical person who's looking to do more and may have outgrown the site as it currently is.
DNN 3 was a great build - in fact I've still got a few websites running 3.1.1 which I felt was the best DNN 3 version and the fastest. After that, the changes started getting put in place for .NET 2 framework since DNN 3 runs on the .NET 1 framework, and over time there were two versions of dnn that were similar, but had different numbers to reflect .NET 1 and .NET 2 framework. so, 3.3.7 ended up being the last .NET1 framework build, and 4.3.7 was the sister copy for a better word that ran on the .NET 2 framework and introduced people to the newer version of DNN 4, and now, we have DNN 5 which can run on the .NET 3.5 framework.
How this affects you is the limited amount of modules available but you might have a work around, but only if the hosting provider will install these modules for you. http://www.inventua.com have a series of flash and media modules which they have provided since DNN 3 and perhaps they can be used.
You can also embed video and flash into the skin and this could buy you some time - In the early days we used to put alot into the skin, rename it and make it custom for that page, to give us the flexibility that wasn't there at the time. It's a bit of work but it might buy you some time until you are able to make a decision on what you need to do.
Most module developers won't support back to DNN 3 as it's quite old. The largest amount of users to date are on the DNN 4 builds, from what I see being offered for sale, and DNN still has here, as their professional version the DNN 4.9.2 build.
You don't have to be 'satisfied' with what you have, but you may make better decisions moving forward when you understand how and why you are where you are and why your hoster is reluctanct to upgrade you.
The mention of 'fake' DNN is confusing to me - I don't see why that comment was made, but you might very well decide that with your own experience and interest in this project, perhaps it might be worth considering upgrading to a new build (of course tI have no idea on how big the current site is so it might not be that easy). By upgrading to a new build you could take advantage of newer methods and keep the data in place or most of it, if it's in a structure that allows you to export and rebuild, and you can modify the skin so it fits later versions of DNN.
It sounds like the site is a few years old - I could be wrong but i would say that it's a few years old, and like anything, is due for review, assessing whether to upgrade or rebuild and the current machine it's sitting on might not have the ram needed for later versions, or might not have the .NET2 framework installed, which sounds like it to me.
I would go back to the ISP if you are happy with them and they are local and ask them what's involved in doing the following -
1 - replicating your build on a single instance and doing this by duplicating the portal and deleting all the other portals from it (I have done this before and it works but not always the quickest thing to do)
2 - exporting your portal and putting in a new instance of DNN on it's own
3 - rebuilding from new.
This doesn't solve your problem but it does give you more information to go ahead and make some 'informed' decisions. I don't think you are using a 'fake or forked' version of DNN and this is a misleading and confusing thing to say when all you want to know is.. why I am stuck on this version of dnn.
Nina