I am curious - how are you creating your basic charity walk web site? Not registration but just the publicity part. For example, WordPress? Or a Website hosting / building service? And so far do you like what you are using?
Also, for collecting donations, is anyone just using PayPal or Google Checkout, and if so how did that go / is that going? Do you find that you need more accounting, like you would get with the more advanced tools, or is this sufficient for smaller events?
The walks I am involved with use full featured software that support pledge events. The software creates both the main website for the event and all of the fundraising websites for each of the participants. The software is also tied into the accounting system of the organization.
As for PayPal and Google Checkout...I would be concerned about using Google Checkout because it appears the purchaser has to sign up for a Google account and be signed in to make the transaction. Online donations are still scary for many and I would be concerned that this would cause them to abandon making their donation. I think PayPal can work since it now offers the ability to pay by credit card, similar to other services. I would offer the ability to pay via a PayPal account, but would not make that the only option. Just my 2 cents.