the fujitsu makes a lifebook that is quite small, and there are some other sony models, particularly the japanese models, that are also in that category of subnotebook.
but a picturebook should do the trick, just beware of running a soundcard through usb on it...i could not get my usbpre to run 24bit on it no matter what, only 16 bit would work reliably. i have also heard of problems with the mini-me and picturebook, which may or may not have been solved with the use of a pcmcia usb card.
pcmcia devices on the other hand appear to be pretty stable, ie. vx pocket, multiset, etc.