You can change the default home directory or default directory "C:\Documnets and Settings\My Name>" by editing your registry settings.
Take backup of your registry before editing it so incase anything goes wrong you can always revert back to origional
Here is what you have to do...
1. Click Start, Run and type Regedit.exe
2. Find the following PATH
HKEY_CURRENT_USER \ Software \ Microsoft \ Command Processor (for only your user)
HKEY_Local_Machine \Software \ Microsoft \ Command Processor (for every user on the machine)
3.In the right-hand column, double-click Autorun and set the Value Data as the path you desire. In your case it should be like this
"CD /d C:\" (without qoutes).
Changes take effect immediately so you can check straightaway.