Why is not all memory used?

[Iain Stevenson]

I upgraded the memory in my 9600 system to 512M (from 320M) recently and 
now it seems not to use all of the memory available.  It also starts to use 
swap after a while even though lots of free RAM is available.  Here is 
/proc/meminfo:

        total:    used:    free:  shared: buffers:  cached:
Mem:  524775424 278798336 245977088        0 68919296 68943872
Swap: 104853504  5517312 99336192
MemTotal:       512476 kB
MemFree:        240212 kB
MemShared:           0 kB
Buffers:         67304 kB
Cached:          64908 kB
SwapCached:       2420 kB
Active:          69008 kB
Inactive:       159512 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       512476 kB
LowFree:        240212 kB
SwapTotal:      102396 kB
SwapFree:        97008 kB

I am running kernel 2.4.19-rc1.  Any thought as to whether this is correct 
behaviour and, if not, how to change it are gratefully received!

  Iain