I had one of these back in the day, upgraded to the maximum.
Basically, it a 1ghz Pentium M with 256MB of RAM soldered. That's right, this thing had soldered RAM before it was cool.
Oh, it also had an nVidia GeForce Go 7300 with 64MB of RAM! But this was pretty much useless.
Between the CPU and low RAM, it's really slow. Without more, it could not decode h.264 AVC encoded video in HD.
It had a wifi card in it's only mini PCI Express slot. You could take that out, and instead put in a Broadcomm CrystalHD card which, with the right drivers, could decode h.264 AVC video up to 1080p. Pretty much anyone that ran XBMC on it did this.
Another neat upgrade was the drive. It had a 2.5" IDE/PATA spinner drive that was super slow. While rare and pricey, there were (maybe still are) some companies that make IDE/PATA SSDs. Either way, even a low quality SSD could saturate the 100MB/s speed of the PATA connection. That made booting a lot faster.
With those upgrades, it made a decent XBMC box. Not good, but decent. Even with those upgrades, it was still utter rubbish at running full OS X.
However, I believe it is still to this day the most elegant streaming box that technically supports 1080P and has composite video output. So if you're one of those suckers that bought a 1080P television before HDMI existed, and you don't like using converters/adapters, this baby is for you!