Hi:
I installed Rockbox on my Sansa clip and while not having all of the Rockbox features, the essentials are covered.
A heads up that Buy.com has refurbished Sansa Clips, V1, for $20. It's tiny, has two gigs of storage and no micro sd card slot. I ordered several to pass on to friends.
It's inexpensive, runs rockbox and you can actually buy one without worrying about getting the wrong version. The conversion instructions are clear and easy to follow.
It's probably not going to be anyone's primary player but Rockbox for $20 is a great deal.
Tom