How can I get Win98 to release memory when an application is closed?

Okay, I'll try to spell this out more clearly for you guys.

When I boot into this machine, I have 30Mb of unused physical memory.

When I look at the "Properties" of a 20Mb .wav file, the unused physical
memory drops to 15Mb.

When I close the "Properties" windows, the unused physical memory stays at
15Mb.

If I open 20Mb file (for instance, in SndRec32), the unused physical memory
drops to 0, and a 5Mb page file is used.

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Hence my original question: How can I get Win98 to release memory after an
application (or the Properties window) is closed?

Note: As I stated as the *first thing* in my original post, adding more RAM
is not an option at the current time; please do not waste time by belaboring
this point.

Thanks,

Jon