The instruction did not say "type ebuild /path/to/foo.ebuild digest", and I'm fairly sure that the name of the package is not digest-anything-- oh, the error says that, as well.
So this is firstly a typo (you should type "ebuild <packagename>.ebuild digest", but if it's a real portage package, you shouldn't be having this problem in the first place, because it should have a digest.
So since I would guess that this is a new addition to portage (kernel 2.4.26_pre6? wow), maybe what you need to do is:
1) an emerge sync to update your portage tree (I had this problem day before yesterday when Wine-20040408 came out; I could see it in the online package list, but my local copy of Portage didn't know it was available to me until I did an emerge sync to update it)
2) use the command ACCEPT_KEYWORDS="~x86" emerge --pretend --verbose gentoo-sources to confirm that if you emerge the most recent kernel you will in fact get 2.4.26_pre6 (the message will tell you what package it would pull, that's what --pretend --verbose is all about);
3) if the right one would be installed, just use the same command without --pretend --verbose, but if it would pull 2.4.26_pre3 or something, do ACCEPT_KEYWORDS="~x86" emerge "=gentoo-sources-2.4.26_pre6" (with the quotes) as shown
here, in the section about how to install a specific version of gnumeric.
But looking at the online package manager, you shouldn't have to do that; if you're not getting 2.4.26_pre6, it's most likely because your local portage tree is old, and an emerge sync will fix it right up, enabling you to do a normal emerge to get the package.
ebuild foo.ebuild digest problem
