Aw.... really sorry to hear it Karen.
Starting with you, no, don't walk it, you'll do more harm than good and be out of action for much longer than if you do what you know you need to, and rest it. Okay, there would be less impact than running it, but you'd be on your feet for much longer, so it's not going to do you any good.
As far as the money you've raised goes, when most people sponsor someone it's either to support the runner and give them a bit of motivation, or because they believe in the charity's cause, or both. I'd suggest telling people what's happened, and offer to pay the money back if they want it. If anyone takes you up on it, I'd eat my smelly running socks! Hope whoever you're seeing today puts you on the road to recovery.
It's so much easier dishing out advice than taking it.
I've messed up my Achillies, not a serious thing but after ultrasound yesterday the fizz says no running until the weekend at the earliest. I haven't been able to run all week, it's a gorgeous morning, I've got brand new sorbathane (SP?) insoles and I've got withdrawal symptoms that are worse than when I gave up smoking and wanted a fag NOW!!!!
Apparently the OH reckons that living with me while I can't run is actually worse than living with someone who's giving up smoking could possibly be