Failure under load on NT Server

Hi,

I am running PHP 4 (release) on an NT Server sp6 with IIS and SQL Server 7.0.

I am using ODBC in order to connect to SQL Server.

The system works well under light load, however under heavier loads 
(25 simultaneous connections) I get an error in the browser ('PHP has 
experienced an access violation 87xxxx').

I am running PHP as an ISAPI extension.

Can anyone help as this is running on a live server and we are 
expecting a heavy load shortly??

PHP is running on the SQL Server machine along with IIS - do you 
think that it would help to move the webserver and PHP to another 
machine?

Thanks in anticipation - I have been lurking on the list for a while 
and I know if anyone can help it is you guys.

Cheers,

Matt