The security steps they've taken are significant, especially in the realm of browsing--the main attack vector for Windows these days, by far. Low-rights IE7 will go a long ways towards the elimination of these threats. Keep in mind, Microsoft has had some lousy security holes for some products, but not all--take IIS 6, for example. Because of their market share and because they are everyone's favorite punching bag, it will be a race to find the first "Vista Virus." Time will tell, but don't rule out the possibility that they could nail it.
I would really recommend checking out channel9.msdn.com--there is a wealth of in-depth information from all sorts of different teams within Windows--kernel, file system, digital media, WPF, networking, printing, color handling, etc. I especially recommend the "going deep" series. You'll quickly find out that there is a whole lot going on in Vista that rarely makes it into the zdnets and pcmags of the industry. It has been really unfortunate how little Vista coverage has gone beyond the interface, the backporting of certain technologies to XP, and the dropping of WinFS. But how do you explain the details of a TCP/IP networking stack in a 2 page article for a casual tech reader? You don't.
As for the graphics... first off, you don't need a 256 MB video card, but you will want one if you want to run the enhanced graphics (Ctrl + Shift + F9 toggles it on and off). Once your video card's memory is exceeded, the UI will utilize your system RAM, so the more video RAM, the better. The video subsystem runs in user mode rather than kernel mode now, also, so a video driver error isn't a guarantee of a reboot anymore.
Describing the graphics as a ripoff... well, that's just silly, I think. Do you really care who "came up with the idea of transparencies" first? Transparencies were supported back in W2K days, but weren't used in the general UI... does that mean it still beat OS X? Because we didn't see Flip3D until recently, does that mean that the Looking Glass team first had the idea of a 3D UI, and Microsoft simply copied them? Who really cares? Transparency in a UI is hardly a technical achievement, nor is it some novel UI metaphor. In fact, it might be better to stay away from it, for the most part. People get really bent out of shape comparing these things. No one gets upset that another car manufacturer copies the "steering wheel and gas pedal" idea--the steering wheel and gas pedal UI metaphor--from another car manufacturer, do they? Of course there are going to be similarities; in fact, I think we count on the fact that there *will* be similarities.
What I think *is* important, however, is the underlying technology capabilities that produce the graphics on the screen. Vista is very advanced in this regard, and leap frogs OS X. Incidentally, OS X didn't introduce many of its advanced UI effects until it iterated through several versions, so the number of years that they've "led" is misleading... does anyone remember what a mess OS X was when it first came out??? Ultimately, it still doesn't necessarily add up to better UI, of course, but the capabilities that are there in an easy-to-exploit fashion for developers--both 3rd party and for Microsoft--are pretty exciting. It will take some time before we see that catch on fully, I think.
Again, check out channel9.msdn.com. It is full of great information--usually in video form.