Installing Netbook MeeGo from a USB stick to an external USB hard drive for use with a 901 often causes drive reference problems on booting.
I solved the drive reference issues by installing from a DVD as follows:
a. download the relevant Netbook MeeGo .img file to a Linux box.
b. rename the .img file to a .iso file and burn a DVD.
c. using GParted delete all data from the external USB hard drive so that the entire drive becomes unallocated.
d. make sure the 901's card reader is empty and that no USB sticks are plugged in.
e. plug in an external USB DVD reader, load the DVD, boot to the DVD and instal Netbook MeeGo.
f. thereafter boot to the external USB hard drive.