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.