I think that Morrowind is worth the buy.
Its is priced down a lot nowadays, only 20 euros or so.
The game is really really cool to play, it is SO huge, I just cant over state that, its just insane.
It also is very easy to make maps and mods (called plug-ins, in the Morrowind community). You can run basicly an unlimited nummer of plugins at the same time, and you can add your creations to the game.
Files are small and you can do what you want.
People are even making a TC based on Lord of the Rings which is supposedly (going to be) extremely large and cool.
It is however a hell of a lot different than Hammer/Worldcraft. From what i can remember, you can just select pieces and put em all together, just save it as a .esp file, and on the Morrowind startup screen tick the box next to "myhouse.esp" or whatever and BAM, you're done. Very easy, although, you can makeit as complex as you want it to be.
You could just make a new trader NPC and script the dude so that he will carry your stuff and follow and defend you.
You can make your own castle, with all the cash and weapons available, thus making the game very easy
Also, most of the doors are teleporters and the inside of a house is in theory a totally different part as the outdoor world.
This allows for some interesting stuff.
For instance, you can make a treestump in the outside world, with a small hatch in it, that leads to the interior a huge and gothic church.
All very fun, if you have a relatively good system.
As a reference:
i have a 2.6 GHz P IV
512 MB DDR RAM
128 ATI 9600 TX
120 GB 7200 rpm HDD
and the game runs almost perfect on my pc, IF i turn shadows off...
But hey, if thats the price i have to pay to be able to fight bizar monsters with cool allies, while flying over a world that will make Peter "LOTR" Jackson drool, who cares?
Conclusion: just buy it, where we go from there, is a choice i leave up to you...