I've used the socket trick before to go down a size on your socket and pound it on to the old bolt.If you have both standard and metric try both theres going to be one that will work nice and tight.If the bolts in the rim don't try grabing it with vise grips or banging a grove in there you'll end up scatching the crap out of it or mabey you don't care because you got new shiny rims.

 

Go to a tire shop, they have the tools to get if off in about 30 seconds, and they probably won't even charge you for it. It's basically a socket tool that they hammer on.