First off, take heart: what determines how quickly and easily you learn Manifold is not the level of GIS experience you have - it is almost exclusively how willing you are to read the documentation in the recommended order.
Seriously, because of the very low price of Manifold we have far more users beginning work with the product who have no GIS experience than we do people with GIS experience. There are three main determinants as to how that goes, two of which you already have knocked off. First, people should have basic familiarity with computers. Surprising though it may be in modern times, there are still some folks who never personally have operated a computer. Manifold is not the place to start. Second, it helps if people are familiar with Microsoft ways, since Manifold tends to use Microsoft nomenclature and to employ Microsoft notions when possible. That is annoying at times to folks who come from other traditions, such as Linux or Mac, but, given that 97% of people on the planet who do computing are familiar with Microsoft ways, to the extent Manifold can re-cycle Microsoft notions it makes it easier for newbies to get started.
That brings us to the documentation thing, which is more important than prior GIS knowledge. Yes, it is certainly true that someone with GIS experience brings a lot to the party. A GIS person already knows what projections are and probably has lots of street smarts related to dealing with things like shapefiles. But all that is for nought if they can't bring themselves to read the documentation to learn how to apply those street smarts within Manifold. In fact, some of the toughest cases in support arise from folks who are used to being maximum experts within some other package and will absolutely refuse to read even one word of documentation on Manifold... everyone knows the type! :-)
In contrast, we have plenty of users who have basic Microsoft Office skills but zero prior knowledge of GIS who plug along and read the doc in the recommended order and do just fine. You can do that too.
To pick up on other comments in this thread, I should emphasize that there is a lot to GIS - not a negative statement but a positive statement about the tremendous power and range of capability you get when you combine visual interfaces with DBMS capabilities and analytics. It's huge value for your money, but that also means there is a lot of substance there in basic concepts as well as a lot of details there arising from the sophisticated control over nuances that users who have preceded you have demanded. That's not all there to make life miserable by making things more complex than they need to be, that's there because the giants, those prior users, on whose shoulders we all stand could see the need for controls and choices to make it simpler and easier for them to make this very powerful mechanism do their bidding exactly as they wanted.
The easiest way to learn Manifold is to accept that detailed, attentive reading and study are required for at least a day or two. Read the topics in the Introduction chapter and also the topics in the Tutorials (those topics show step by step how to do the image server thing) and Examples chapter. Actually read them attentively - don't skim - and you'll see that after an initial period of panic and near-vertical learning curve it all starts to fit into place quite rapidly. Seriously, to get your head around something like this in just a couple of days instead of the months or years of study such things took in the early 1990's is real progress! :-)
I'd also encourge you to buy the training materials from http://www.gisadvisor.com, which is a third party company unaffiliated with Manifold, but very highly regarded in the Manifold user community. It's a lot to ask to spend a couple of days plowing through written documentation, and viewing the training videos from gisadvisor is a great way to take a break, get the information from a different perspective, etc.
Also, start with some simple projects using data of interest. GIS is very visual and a lot of fun so the sheer visual pleasure of it is a great way to fend off the tedious documentation blues.
Last, but not least, keep in mind that ESRI does not exist in the mainstream, not at all. They have majority share in legacy markets, but near-zero share in markets where Manifold is expanding faster than all other GIS vendors put together. This makes sense, because of the 500 million or so Microsoft Office users there are many who are interested in GIS at $245 a seat but virtually none who are interested in GIS at ESRI pricing, so Manifold far outsells ESRI on a unit volume basis. It's true that there is a lot of inertia in legacy markets, but even that is changing fairly rapidly as government agencies, counties, cities, etc., discover they can deploy a dozen more Manifold seats for less than the cost of ESRI maintenance. Plus, they know with Manifold they get 64-bit operation, multicore capability, CUDA, Vista and all that other modern stuff they don't get with ESRI.
Hope this helps!