I built this machine about 5 years ago. P4 1.8, 1.5 gb ram, a radeon 9800XT. Honestly, with all the powerful new stuff out there I'm surprised mine even loads webpages.
However, recently since I've been looking into finally getting a new computer I've been relearning what is all out there and what is best. What i've come to find is that SLI is VERY buggy and only works with a handful of applications. The rest all just use your primary card and don't even know the other exists. A similar occurance is happening with the dual and quad core CPUs but it is less common as more programs will work with multithreading. Intel is destroying AMD. NVidia is destroying ATI. Both Intel and nVidia are releasing their next gen chips and boards but they aren't even necessary because the number of applications that will use them can probably be counted on one hand right now. And since Intel and nVidia are so far ahead of their AMD rivals (AMD owns ATI) they pretty much hold a monopoly on the high end systems which is why the top of the line 768mb 8800 Ultra costs upwards of $650.
And you thought 750w was big? Most systems that poeple will build themselves that want any type of future compatability will be housing 1000w power supplies, some even higher, since a dual 768mb 8800 GT setup will use up every bit of the 1kw.