Is it possible to run two Linode configurations at once?

No. You cant.

Think of your node as a phyiscal server. It will act the same as one. So you can only be booted into one OS at a time.

You'll need to buy another node if you want to have another one alive and running.

Thanks Internat. Quick response (Y).

No problems :)

Remember that Linodes are pro-rated (to the day, I believe). So if you only need a second instance for a day or two, you can add one to your account, use it, and cancel it. A 360 comes out to roughly $0.67 per day, so it's pretty cheap if you just need another instance for a day or two!