I have a windows forms app that does a lot of number crunching. In
certain calculations I get an OutOfMemoryException, even though the
Windows XP performance monitor reports 1GB of physical memory available
(2GB total). There is no stack trace available, so I can't pinpoint
where the problem is occurring.

However, if I try debugging the app through Visual Studio, I do not get
the out of memory problem! Does anyone have any idea why I'm seeing the
different results in debug/release mode? Any idea what I can try to do
to pinpoint the source of the problem?

Thanks
Akash

Here is an answer for your question as to why there is OOM in spite of
perfmon showing that you have memory.

http://blogs.msdn.com/tess/archive/2005/11/25/496898.aspx.

I guess probably the heap is fragmented.

Preventing Exceptions from bringing down app
SuppressFinalize in Dispose confusion
Obtaining a "CoClass" from interface in .NET for the purposes of sinking events.
Converting to big -endian
KB913384