Hi alinasept (and others),
Did you ever find a solution?
I am having the same challenge.
Today I purchased a Sansa c250, knowing that I could put the Rockbox firmware on it.
However... for some reason I cannot get the bootloader to see the device.
I have Vista Home Premium and have done the following...
After following the manual (and I think maybe the manual could be clearer about how to put in MSC mode, and if needing to change file to FAT32)...
-- Set the c250 in MSC mode (UMS mode) by:
1)turning off the c250
2)turning it on
3)putting the hold button into lock
4)pressing on the Previous/Rewind button WHILE plugging in the USB cable
(the USB cable already plugged into the computer's USB port)
as indicated in these two links
http://www.anythingbutipod.com/forum/showthread.php?t=21421http://forums.sandisk.com/sansa/board/message?board.id=view&message.id=288&query.id=10213-- I also read that recognition of the c250 depends on the disk layout
http://91.191.140.131/irc/rockbox-20070921.txtthen found a thread that spoke of making sure the sansa disk layout was formatted in FAT32
so I did that...
http://forums.rockbox.org/index.php?topic=12800.15-- Also, I have turned off  “User Account Controlâ€.
-- No cards in the reader.
-- Have run Rockbox Utililty and all other downloaded files can now be found on the sansa.
EDIT
-- Also found this thread that spoke of checking the partitions on the c250
http://forums.rockbox.org/index.php?topic=12239.15and, after searching found the TestDisk program,
which seemed to indicate there was but one partition on the c250
so maybe my problem is that I do NOT have the needed hidden partition
and now need help creating it?
END EDIT
2nd EDIT
After reformatting to FAT32, the disk manager showed FAT32 format on the c250
Yet, when looking at it just now, it doesn't show up in the top screen of
Vista's Computer (right click) > Manage > Storage > Disk Management window.
I can drag and drop music files to the device... so it works in some fashion...
I'd better stop before I do something really silly.
END 2nd EDIT
... and yet I get the same error messages when running
either the sansapatcher.exe  or the Rockbox Utility for sansa.
sansapatcher v0.6 Error Messages:
sansapatcher v0.6 with v4.0 bootloaders -
Dave Chapman 2006-2007
this is free software; see the source for copying conditions. Â There is NO
waranty; note even for MERCHATABILITY or FITNESS FOR A PARTICULAR PURPOSE.
[INFO] Scanning disk drives...
[ERR] Â No E200s or C200s found, aborting
[ERR] Â Please connect your sansa and ensure it is in UMS mode
[ERR] Â Please refer to the Rockbox manual if you continue to have problems.
Press ENTER to exit sansapatcher :
“
Rockbox Utility Error Messages:
It seems your Bootloader is already up to date.
Do really want to install it?
(I choose “OKâ€)
In a Progress Window...
Starting bootloader installation
Searching for sansas
No Sansa found
Ideas of what I could do next?
Thank you.