AussieJohn: Thank you so much for taking time to give me such detailed instructions - Very kind of you. OK, just before seeing your reply, I was "fooling around" with couple of things on my own, and here is what solved the problem (well, I did a number of things, and maybe something else contributed to the solution also, but the following is the "thing" that really did it):
Open MCC -> Local Disks -> Mange disk partitions, then open the sda (my USB hard drive) tab, then click on Toggle to Expert Mode button and then click on Options button and tick the "user" check box (this allows an ordinary user to mount the file system). And that was it - it WORKS now.
Thanks again John for your help.
Best regards to all, and BIG CONGRATULATIONS TO MANDRIVA for an excellent product.
serge.