I just installed Rockbox on my Sansa e260, the other day after seeing it on slashdot, and it has worked great so far.
I bought a CD from a local used music store, brought it home, and promptly ripped the CD to my PC via Windows Media Player. I then proceeded to sync the newly ripped files to my Sansa, everything went smoothly.
The problem is that now that the files are on the flash player, the library hasn't updated!
I tried searching through the options in the player, as well as the manual, but I can't seem to find a "rebuild library" function anywhere...

I have explored the device and have confirmed that the WMA files
(as well as a few MP3 files that I got off the internet, also added at the same time)
are indeed on the drive, windows media player confirms this as well.