Head on over to Mozilla.org and download Mozilla. It has an editor. If you are somewhat (mildly) proficient with HTML, or able to get around a simply WYSIWIG environment, you can use that program.
First, get onto your idisk by accessing
http://idisk.mac.com/username/
Second, download your page you wish to edit.
Third, open it in Mozilla's page editor by going to File>new composer window, then File>Open (or something like that).
Fourth, save your edited page on the local disk.
Fifth, delete the page on your idisk.
Sixth, upload your new page you saved.
Seventh, test and repeat steps as necessary.