The day may come when you find that you need to move the package share (SMSPKGC$) to a different drive - say from the C: drive to the D: drive, and you don't want to have to recreate any existing packages or advertisements. Should that day come, Rob Morris wrote up some steps you can follow to get that done:
Note that the permissions outlined above were the permissions in my test environment, so those in your environment may be different. It is also recommended that the D: have more free disk space than C: at all times. Another option would be to place the NO_SMS_ON_DRIVE.SMS file on the C: drive to prevent SMS from placing any components on that drive in the future.
J.C. Hornbeck | Manageability Knowledge Engineer