Take heart it can be done:
http://www.plymouthhospitals.nhs.uk/Pages/Home.aspx - check out the source - look no tables.
or if you prefer why not admire:
http://www.wise-woman.net/Pages/default.aspx
Sharepoint and accessibility - two problems first what do you have to do ? and second how are you going to do it- well it depends who you ask:
as can be seen from this very clear article http://www.21apps.com/sharepoint/sharepoint-accessibility-is-moss-2007-accessible/ its a slightly mixed up picture.
But here is a check list for the various standards that one might hope to adopt http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990324/full-checklist.html
so can it be done?
well microsoft have a whole site dedicated to the proposition that you can http://msdn.microsoft.com/en-us/accessibility/default.aspx
if you want something a bit more graspable have a look at this word document giving some best practice about the subject http://go.microsoft.com/fwlink/?LinkId=121877
The Microsoft/AKS accessibility standard lives here http://aks.hisoftware.com/index.html
My fear with some of this stuff is that it is really important one adopt A STRICT attitude toward editing pages. i.e. enforced change management, though notice that neither of the sites at the top use the STRICT tag in their XHTML - this is fine for public sites. Big intranets intranets are easily messed up by the keen user with a copy of SharePoint Designer - what is a fellow to do?