Problem In Using Linked-servers While Running MSSQLService Under Low-priv. User Account

Hi.
While hardening a ms-sql2000 , I faced with a problem and I`m completely lost !
few days of reading and google searchs didn't gave me any hint...

Here's the scenario :
Ms-sql is connected to Oracle , through "MS OLE DB provider for Oracle" .
By default MS-SQL runs as SYSTEM , but even if we change it to a "local admin"
account , everything works fine .
The problem is that it's not wise to let sqlservice to run under privilaged accounts such
as system or a member of 'local administrators' . So I tried a normal local user on the
host running sql . I fixed every related problem appearing because of using a limited user
account and ms-sql works fine in all aspects but one !
While using normal-user account , sql-server fails to load linked-servers and this error
pops up in enterprise-manager :

"OLE/DB Provider 'MSDAORA' IDBInitialize::Initialize returned 0x80004005:
The provider did not give any information about the error."

I've tried much to find root of this error ( including any comments from related KB articles... ) but no luck . My guess is that , using OLE requires administrative privileges on host , and as I'm running SqlService with normal user, it fails to use OLE. So I should give requried permissions to the user running SqlService . But the problem is that I've no idea where/how I should do that. I've already tried some registry/file permissions but non of them helped me.
Some where I red that using ODBC instead of OLE may help , but that seems fail too !

*Note that I'm almost sure it`s a problem OUT of circle of ms-sql , meaning any modifications should apply OUT of ms-sql , because simply giving local administrative privileges to the user, fix the problem.

Any comments?

regards
Hamid.K