IUSR permissions problem - C

I have a problem that started out with SQL server, but tracing the cause
seems to lead back to a very general windows issue.  In summary, when trying
to execute a linked server query to an Access database, invoking OLEDB Jet
drivers,  from a web application, the command fails because IUSR does not
have the right permissions.  (If IUSR is promoted to the Administrators
group, the command works.)

The problem is -- figuring out what permission is needed and where.  When
the command fails (IUSR normal permissions), filemon records these events
among others:

5:03:01 AM    sqlservr.exe:1232    QUERY INFORMATION
C:\DOCUME~1\NETWOR~1\LOCALS~1\Temp    ACCESS DENIED    Attributes: Error
5:03:01 AM    sqlservr.exe:1232    QUERY INFORMATION
C:\DOCUME~1\NETWOR~1\LOCALS~1\Temp\    ACCESS DENIED    Attributes: Error

When the command succeeds (IUSR promoted to administrator), filemon records
these events:

4:56:52 AM    sqlservr.exe:1232    QUERY INFORMATION
C:\DOCUME~1\NETWOR~1\LOCALS~1\Temp    SUCCESS    Attributes: D
4:56:52 AM    sqlservr.exe:1232    CREATE
C:\DOCUME~1\NETWOR~1\LOCALS~1\Temp\JETE108.tmp    SUCCESS    Options: Create
Access: 0013019F
4:56:52 AM    sqlservr.exe:1232    QUERY INFORMATION
C:\DOCUME~1\NETWOR~1\LOCALS~1\Temp\JETE108.tmp    SUCCESS    Length: 0

Because of the way folder names are truncated, it's hard to know exactly
what folder is referred to, but in any case, no such folder can be seen in
the file system (even with folder options set to show hidden folders).  I
tried the following:

1) Giving IUSR full control over the "Documents and Settings" top level
folder;
2) Creating "/Network Service/Local Settings/Temp/" and "/Network User/Local
Settings/Temp/" paths in that folder, and giving IUSR full control.

Neither of these helped; the command still fails if IUSR is not an
administrator.

So -- how is the Jet driver (when the command works) accessing a folder that
seems not to exist ?  How do I find this folder and adjust its permissions so
IUSR can use it?