Is there a USB interface for a RadioShack 22-812 Digital multimeter?
RS232 to USB is very common. Here is an example:

http://www.amazon.com/StarTech-com-RS232-Serial-Adapter-ICUSB232/dp/tags-on-product/B000067SNB

Expanding a little, these cables will create a virtual com port on your computer. So when you plug it in, even if there isn't anything connected to the cable, drivers will be installed and a virtual com port will be generated. Because of how it does this it looks like you just plugged the serial cable into the computer directly.