I use the same motherboard for my Pentium M rig. It hosts a GTX-260 Core216 and a PM 745 @ 2.4GHz. Very fast and stable combination. In fact, it's always felt (and benchmarked) faster than any of the single-core K8 machines I've built. I'm not sure how much of this has to do with Win7 being the OS; my single-core A64 systems still run XP.
The ICH that the Speedster uses actually supports AHCI, despite being only a SATA-150 controller. You could use something like a 60GB SSD as your boot drive if you wanted to.
For memory, I'd recommend dual-channel DDR2-800 memory instead of DDR1-400. DDR2-800 will downclock to 533MHz for a perfect 1:2 FSB:DRAM ratio. At 533MHz, most PC6400 modules will let you run them at CAS 3-2-2-8, which will boost performance.
Not sure what your budget is, but I've always wanted to put my PM rig in a Silverstone Temjin TJ08-E mATX case. It's currently in an Antec 300 midtower, which, while definitely not as sexy (or quiet) as the Temjin, does the job.
I purchased two Speedsters, neither of which came with a proper S479 HSF. I had to remove the heat spreader from one of my old P4s, attach it to the PM, and then mount a standard S478 HSF on it. This seems to work well, as CPU temp never exceeds 34 deg.