If I were a graphics designer, I would not buy nVidia. Fdz probably owns, or will buy a kick ass 19- or even 21-inch monitor. What he needs then, and certainly if your in the graphics bussiness, is a good RAMDAC and decent output signal quality. If this were the only criterium, I'd go for Matrox, but since then you get like no 3D-power, ATI would be the next best choice, I think. Unless he goes with a professional nVidia based card (Quadro-line). Maybe those have better outputs, but I'm not aware of that.
If he goes for a DVI-signaled TFT-panel, though, I don't think these restrictions apply, since data transfer is done digitally. So I guess then nVidia would suffise.
SSE2 won't be of much use to graphics-handling. I think that kind of programs uses only integer calculations (correct me if I'm wrong), so SSE2, wich implements 64-bit floating point instructions, is of no use. Only good old MMX will improve performance here, which both P4 and XP have. Theoretically the P4 would be a good choice, since it has got a very fast set of ALU's, running at double clock speeds. But they are told to be withheld by a slow decoder and too many pipeline stalls and stuff. Though I don't know wether there will be many of those in graphics manipulations.
For the video edoting, I don't know what to think. The XP seems to be the ruler in Mpeg2 (DVD)-type video and the P4 is a clear ruler in the Mpeg4-world (DivX, Xvid and stuff thelike). But the P4 is close when coupled to RDRAM when it comes to Mpeg2.
Maybe even a dual proc setup is to be considered. The Xeon-system are bloody fast (even with DDR, look at <A HREF="http://www6.tomshardware.com/cpu/02q1/0203131/index.html" target="_new">Tom's article on this</A>, but darn expensive, too. Athlon MP's are very fond of electical current and can be used as a auxiliary heating in your room, but are very good performers, certainly in comparison to their price. If Fdz is interested in this, he might look for some older threads about this. Like <A HREF="http://forumz.tomshardware.com/modules.php?name=Forums&file=faq¬found=1&code=1" target="_new">this one</A>, or <A HREF="http://forumz.tomshardware.com/modules.php?name=Forums&file=faq¬found=1&code=1" target="_new">this one</A> and many others.
Greetz,
Bikeman
<i>Then again, that's just my opinion</i>