The folks over at openspf.org have been working on a revamp of their website. This afternoon, they flipped the switch to move to the new version of the site. All of the previous content is now found at http://old.openspf.org/. This includes the SPF Wizard, which is a web-based tool for creating SPF records to insert in your DNS. For now, there seems to be a redirect in place, but there is supposed to be a new version of the wizard coming soon.
If for some reason your current bookmarks don't work through the redirect, now you know why. That shouldn't be the case, but you can always manually replace the www.openspf.org with old.openspf.org to get to the content.
You can, of course, use the Microsoft Sender ID Wizard to create your SPF and Sender ID records. However, you need to be aware of the fact that Microsoft's Sender ID standard, while remaining mostly compatible with SPF, has been deliberately written to break the SPF standard in what Microsoft considers to be a minor way; I'll explain that in a later post. In the meantime, if you just want an SPF record, you can use Microsoft's Sender ID Wizard and just tell it you want to work with the v=spf1 record only.