Virtual memory low

First off Its’ a compaq with 1800 AMD,512 SDRAM.60gig HD runing XP Pro.this just stsrted about a week ago It comes up in the lower right it tells me virtual memory too low windows will now reset ok so I let it do it’s thing for about 10min.or so go back in an check on it sure as I’m sitting here now I got less virtual memory this will happen about every hour even if I let it set idle The only thing that was changed lately is I added DSL that uses a USB port but it didn’t start this right away