You can control what devices are allowed to be installed to a certain degree with Group Policy (only available in 7 Pro and higher) it's quite fiddly depending on whether the device has been installed before or not, and requires editing the registry - tbh it's often more agro that it's worth.
Otherwise you're looking at a DLP solution which are aimed at business/corporate users and hence are not the cheapest applications around, something like DeviceLock for example, www.devicelock.com.
I want to lock the USB ports on a Win7 32bit PC. I have set up Acronis backup software to save to a portable hard drive. how do I lock down apart from a specific item of hardware.
Well that's interested....Thought you had to register to post....
Like DA mentioned, there isn't a easy consumer method out there in order to only allow control for certain USB ports. You might be able to go into the BIOS of the computer and turn some of the ports off there but it will depend on your type of motherboard and if the option is even supported.