Summary:
On db machine:
1) create user IUSR_name-of-other-computer-goes-here
2) Using the policy editor, set IUSR_name-of-other-computer to have local logon.
3) Set "full control" privileges on the .mdb file for IUSR_name-of-other-computer
On the IIS machine
1) create a DSN for the db, point it to the file on the db machine.
That will make it work :: my situation was in a windows 2000 advanced server-only environment; I know it works here, my site used to run exclusively off it [only partially now] .. http://rand0m.org.
There are a couple FAQs on the web detailing this, but they are rough to find. I'll see what I can do.