Autocad 2004 is not compatible with Windows Vista according to the system requirements.
You could try running it in XP mode, you can simply right click on the program's icon (it may be on the desktop, or in the start menu, either or is fine).
Once you right click on the icon, click on properties at the bottom of the window that comes up.
In properties, click on the Compatability tab. Check 'run this program in compatability mode for' and select Windows XP in the drop down menu. Also at the bottom of the comatability tab, check 'run this program as administrator'.