InfoPath 2007

If you run SQL Server on an Office SharePoint Server front-end Web server (for example, in a single-server evaluation deployment), the ASP.NET cache will release system memory at a lower threshold than SQL Server, which could result in InfoPath Forms Services memory starvation.
ASP.NET employs a strategy of targeting maximum Internet Information Server (IIS) memory use of the lessor of either 800 megabytes or 60% of available physical RAM. These settings are configurable in IIS manager. ASP.NET also monitors physical RAM use, not just for the w3wp service, but for the entire system. When 80% of the physical memory on the server is committed, ASP.NET begins periodically dropping the oldest and lowest priority 5% of the cache. When 85% of physical memory is committed, ASP.NET will drop 50% of the cache periodically. At 90% or more, ASP.NET aggressively trims the cache and sets low limits on the maximum number of entries, which remains in effect until ASP.NET reassesses memory pressure on the server and raises the threshold.
The memory usage threshold for SQL Server is higher by default than the ASP.NET cache. In this scenario, SQL Server will never release memory because the ASP.NET cache will already have released memory before the SQL Server threshold is reached. This can lead to a condition in which the throughput of InfoPath Forms Services is reduced with a subsequent impact on performance.
To mitigate this issue, you should configure SQL Server memory limits manually when SQL Server is installed on the same server as Office SharePoint Server . For more information on adjusting SQL Server memory settings, see the article Server Memory Options
on the Microsoft Web site.
http://technet2.microsoft.com/Office/f/?en-us/library/0e9966df-e374-4df5-b3be-9848c78f9ca71033.mspx