I finally found the trick to grabbing old Geocities pages before they vanish: the Wayback Machine's CDX API
Last month I was trying to save a fan page from 1998 that had a spinning mailbox GIF and a hit counter, and the normal Wayback search kept timing me out. A guy on a mailing list pointed me to the CDX API, which dumps every captured URL for a site as a plain text list. I pasted in the address and got 412 snapshots going back to 1999, then loaded the oldest one in the browser. The best part is you can filter by date, so I grabbed the March 1998 capture and the guestbook still had all 60 entries. If you want the exact URL format I used, say so and I'll post it in the comments.