Noone has mentioned building the SPF strings :) I found this a while back:
http://www.anti-spamtools.org/SenderIDEmailPolicyTool/Default.aspx
It's a nice little (online) wizard from MS, which allows you to build the string without having to work out a geekcode-look-alike. AFAIK, they don't store info - just show you the SPF for what you enter.
Be carefull. Sender-ID is not SPF.. Microsoft took SPF and added some changes to it (which alot of people in the SPF "community" think make it worse than simple SPF by itself.). Sender-ID has their own records (see nslookup -type=txt spam.co.nz). but will use the SPF records if there is no SenderID record (spf2.0) and this may make Sender-ID give false possitives at rare times. (the reusage of Microsoft of the SPF tag is what SPF people don't like), but when everyone starts using the new RR of "SPF" instead of TXT for SPF., microsoft can do what they want, as it was given for SPF not Sender-ID). Thanks Craig