Windows XP seemingly out of resources but plenty of free RAM and swap available

"The term ""resources"" or ""system resources"" on Windows refers to various objects (such as window handles) inside the operating system. Windows limits the space allotted to resources, so that they cannot use all of system memory. That is why you have plenty of free memory but not enough resource space.

Mark Russinovich and David Solomon (of Winternals and Sysinternals fame) have written a book that details the guts of Windows thoroughly: Windows Internals. The fourth edition covers Windows 2000, XP, and Server 2003, and it is available by itself or as part of the Windows Server 2003 Resource Kit. The fifth edition will be released in June 2009, and it will cover Windows Vista and Server 2008. One or both of these volumes may be of help for you, but be warned: This is not just a Saturday-afternoon read!"

Did you install some kind of "tuning software"? Most of these fiddle around with settings they should not. And most apply settings which only improve benchmarkable performance but reduce real workload performance (eg interactivity) by turning the knobs of the memory manager.