Available Memory vs Physical Memory

I have a Inspiron 1501 laptop that was running very slowly so I installed a new 1 GB memory card in addition to the original 512 mb memory card.  The system is running much better now, but I decided to check the "System Information" summary and it shows Physical Memory 1024 MB and Available Memory 447 MB .... does this indicate a problem?  I checked the System Information before I upgraded and it showed something like Physical Memory 512 MB and Available Memory 124 MB.  I've heard of some worms which take up address space or something and consume a good portion of the memory leaving only a fraction of memory for system operation.  What do you think, do I have such a worm?  If so, how do I get rid of it so I can get max performance?  Thanks

Sounds like Windows Virtual memory is doing its job.   Windows likes to use as much Physical memory as allowed.  It may be set as a percentage of total physical memory.  Hence, as you increase PM, you increase the amount used by Windows and reduce the available PM.