It is very difficult to state exactly what constitutes the 'best' configuration for any version of NX. Note that while this might sound trite, generally speaking, the 'best' configuration is almot always the most expensive one that you can afford to buy.
But to be a bit more specific, don't try and save money on things like putting less than the maximum amount of memory that the system will support (you may have to temper this a bit when dealing with 64bit system, but it's certainly true with 32bit).
Also, if you have the option, pick hard drives with the fastest speed (in RPM's) as well as the biggest cache and smallest seek time. And don't skimp on the graphics card either, although the ones touted to be the high-end for gaming may not buy you as much for things like CAD. Generally speaking, you should get a professional grade graphics card and not one design JUST for gamers.
Note that the cost of a Spaceball, no matter what model you buy, will pay for itself almost immediately.
And large format (24 inch or better) high-res monitors generally are a good investment, but I wouldn't put it ahead of memory or a fast disk drive.
As for the CPU itself, once you get past either a dual-core or a dual-CPU, the benefits seen by NX are pretty well already there, so don't waste money on quad-cores unless you might be using this workstation for more than just NX, particularly if you're going to be running multiple applications at once.
As for the OS, at this point in time, if you're buying new, go for 64bit. And for all it's faults, it's till pretty hard to beat Windows XP Professional, although a lot of people like the look and feel of Vista, it's just that the corporate world is still firmly on Win-XP.
Anyway, while this doesn't give you any brand names, it at least should help when you start comparing spec's and looking at where you're putting your money.
John R. Baker, P.E.
Product 'Evangelist'
NX Design
Siemens PLM Software Inc.
Cypress, CA
To an Engineer, the glass is twice as big as it needs to be.