New Case

[koshman]

150W is a lot. I had Pentium Dual Core E5200 and NV 8800GS, 4GB RAM, 2 HDDs and an optical drive. Both the CPU and GPU moderately overclocked and it took about 120W at load at the power socket. That was with 80+ Seasonic PSU, so I guess with Pico PSU with high efficiency it could be around 100W.
Based on this I would say any dual core system with a single graphics card would happily work with 150W of power. There are also 45W quadcores out there, which would work too, I'm sure. Midrange CPUs are actually getting more and more power efficient. The problem could be with GPUs where the delta between idle and load is widening. But something like AMD 5770 (5650/70 or whatever's coming out...) should be ok and they have great power/performance ratio.
I don't have experience with other than x86 architectures as far as power consumption goes.

Edit: considering that you're limited to low profile graphics cards, I would say that the power consumption is not a concern at all. With a LP GPU, you can have a quadcore with numerous drives and PCI cards and still be easily under 150W.

[koshman]

The most powerful (performance-wise) PCI-E GPU I was able to find is Radeon HD4650.  It is undoubtedly the fastest, although the LP versions only use DDR2 memory. nVidia doen't have a comparably fast LP offering (the best they have is GT220). Based on the reviews the HD4650 doesn't draw more than 30W at load.
I don't know if it's the most power hungry, but I would say none of the LP graphics cards would go significantly over 30W.

AGP low profile GPUs available today (at least new) are really low end - NV 6200, Radeon HD3450 etc. I doubt any of them would draw more than the higher performing PCI-E offerings.

[koshman]

Yes, pretty much The new AMD mid/high range offering HD5850 is 24cm long so I don't think any of the LP cards would be 23cm or more, but you better check.

Edit: just a correction to the above performance assumtions - GT220 with DDR3 might be actually close in performance to HD4650 with DDR2, but I haven't seen a direct comparison,

As for the height - I haven't measured it myself, but I don't have a reason not to believe what's written in the PDF. Btw, Wikipedia says the same - max card height is 64,41mm and max bracket height 79,2mm for LP cards.