In my ignorance I purchased a DVI- dual link cable to replace a failed DVI- single link. My 20" LG only takes a single link connection. Can I just cut the two extra pins and use the cable anyways?

Try Radio Shack...they have a Monster version for about $99, then their own brand for about $12.99. Just make sure what you need is the DVI-I, and not regular DVI. DVI-I won't fit into regular DVI.