"who wants a blog written in asp.net 2.0 and must use ms access"
So, if I understand correctly, your client wants you to write a blog-type site or module but wants you to store the blog's data in msaccess? is that correct? or am I mistaken and your client has an existing blog sire or module that uses msaccess to store it's data.
If it's the former, and you will be writing a new module for use in DotNetNuke, you can certainly store your module's data in msaccess or any other database. DotNetNuke stores all of it's data in a Sql Server database, but each module can program it's own datasource.
If you want to take advantage of the exisitng blog module, all of the source code is available, all you would have to do is modify the data layer to read/write the blog data to an access database. Be aware though that creating a custom version of a core module will make upgrades difficult.
I would be interested to know why msaccess is a requirement? is it because of your client's hosting environment? do they not provide Sql Server? maybe a different host would be a better solution :)