In my quest for the missing "Storage Devices" in the KInfoCenter of version 3.5.8; I finally came across an acceptable solution. I installed "gtkdiskfree" (since I could not find KDiskFree) and that is very much equal to what I used to see on opening "Storage Devices" under KDE v.3.5.3 ( which was probably opened by KDiskFree in former KDE versions like v. 3.5.3 ). So I hope this is of any help to others as well.
In KDE 3.5.3 one gets to the Storage Devices through KInfoCenter where one can view the used space on the different drives. Sadly in KDE 3.5.8 the Storage Devices have disappeared in KInoCenter. How can one get this feature back ?