How to give permissions for ASPNET user

[axnfan]

I have an application using Asp.Net and MS-Access.
access file resided in httpdocs/db
I have given modify permission to IUSR_domainName
But still I get permission error.

How do I give petmissions to ASPNET & NETWORK users. They are not listed in the users list.

Thanks in advance

Regards
Alex