In the help file under 'Advanced Configuration - Fine tuning' a settings.ini file is described.
I created this file with the 'showpartitions=1' parameter but it doesn't work here.
I can only select the windows partition (i.e. drive C:\) as 'Cache file location' when a 'System Memory' cache is created.
The settings.ini file was placed here:
C:\Users\All Users\eboostr\settings.ini
with content:
[eBoostr]
showpartitions=1
my system: Win7 64bit RC, 3 x Samsung 1GB HDD, 6 GB RAM, 2 GB eBoostr System Memory cache