I want to uninstall 10.5.7 Mac os x update & go back to 10.5.5 or 10.5.6

Lately, updated, from 10.5.5 to 10.5.7. in that I had used Combo update, downloaded frankly from Apple. Initially , backed up to a Firewire, Western Digital Bootable Ext. High Definition , through Super Duper, then ejected the HD. Everything was going fine,all of a sudden the WD ext. HD did not turn up on the desktop but strangely did emerge in Disk Utility Window , so when I clicked on Info for the ext HD, it displayed the connection ID #, and all specifications, showed as Bootable, & writable, as well , please help me out .

Please restart the iMac; this step more often than not sorts out this kind of issue. But, things may go worse, now, the Western Digital , does not show up, in Disc Utility window , so you can restart in the Safe Mode, and so you can check out if the issue is still there Can you tell me that whether the Western Digital ext HD, light is on or not , or can you experience any sort of noise , I am asking here about the clicking noise .

First, can you check the drive on another Mac? Have you called up WD tech support for help? If you boot from your outer clone does the problem stick with?If you are looking for downgrade you have two choices. The first is to boot from your backup, remove the foremost drive, then restore the clone to the main drive. The second is to perform an archive an install

There was something mentioned about the archive and Install will NOT remove your hard drive, but you have to have keep sufficiently vacant storage for a second OS X installation which can be from 3-9 GBs depending upon the version of OS X and selected installation options. The free storage prerequisite is over and above usual free space requirements which ought to be at least 6-10 GBs. Read all the linked references that are there in the Apple care cautiously before going on.