Quick solution: use regedit, search for SYMTDI and remove it from any instance of DependOnService:
DependOnService = "Tcpip Afd NetBT SYMTDI"
Then reboot and dhcp client should now start.
To use regedit:
==>Start ==>Run ==>regedit
==>Edit ==>Find
find: ==>SYMTDI
Keep hitting F3 until you find a key that has a value line of:
DependOnService = Tcpip Afd NetBT SYMTDI (these are for DHCP service)
(we found 2 instances)
or
DependOnService = Tcpip SYMTDI (this one's for NetBT service)
(we found 1 instance)
==> ==> (double click) DependOnService
or
==>DependOnService ==>Edit ==>Modify
Edit the "Value data:" section and remove the SYMTDI entry
==>OK
Then, F3 to repeat search for SYMTDI, looking for any more
DependOnService lines that include SYMTDI, removing it.
Then close regedit and restart machine.
Note: if you re-install Win XP from the Microsoft CD's, you will not have Norton installed. You will note that Norton AntiVirus (NAV) will not be installed. If you search with regedit, you will not find any references to SYMTDI. It is the installation of NAV that inserts the SYMTDI references. It is then the fact that NAV doesn't cleanly uninstall that causes the problem. Thanks Symantec! :-(
(Note: answer to this problem was found by a search in "Google Groups" with the search string "SYMTDI service". Thanks to those that post answers.)