In a Windows operating system, 3.x to the horror that is Vista, out of
memory warnings do not necessarily have anything to do with available
physical or virtual memory. In fact they rarely do.
Out of memory warnings usually refer to dwindling system resources, the
pointers that the OS uses to keep track of things. While successive versions
of Windows have improved on this it is still a problem for many reasons.
As someone pointed out many programs do not release their resources, as well
as the memory addresses, they were using after you close them. This used to
be a major issue with MS Word, to name one. Itunes eats up alot even when it
is not running (all praise the great programmers at Apple).
When you purge memory in Photoshop you are forcing the release of both RAM
and system resources that PS was using. Would that other programs allowed
the same. There are shareware programs that say they are able to do this as
well.
If you are getting frequent out of memory messages it would behoove you to
see what background processes and programs are running that are eating
memory and system resources. The one GB of ram in your system, while not
optimal, is sufficient for running files of the sizes you mention in
Photoshop in Win2K.
Not to alarm you but I would run several anti-spyware and an anti root-kit
program to see if that might be an issue.
You also need to check what is loading when you boot your computer--the
WIn2k version of msconfig.
I would also highly recommend you get a copy of WInXP, home or professional,
while you still can. Vista with the current beta service pack is still slow,
incompatible with too many programs and lacking stable drivers for too many
peripherals. However I will admit that CS3 runs reasonably well on Vista,
but time by your stopwatch slower than XP for any disc access operations
(and what does not access the hard drive?).
The MAC OS has comparable memory limits but MAC users tend to single task.
install less programs (there are far fewer programs for them to install),
and, while Leopard is actually more vulnerable to malware attack than XP or
Vista, so far it is not threatened by malware because businesses do not run
on Apple and the overall market share is too small to bother with.