[ale] System losing memory

[Jim]

I have a Centos 4.4 system that periodically runs out of memory and swap:

Tasks:  70 total,   1 running,  69 sleeping,   0 stopped,   0 zombie
Cpu(s):  2.1% us,  1.1% sy,  0.0% ni, 81.2% id, 15.6% wa,  0.0% hi,  0.0% si
Mem:    483356k total,   468160k used,    15196k free,    10132k buffers
Swap:  1048568k total,  1048568k used,        0k free,   365392k cached

I can't even run a cc command.  The -b output of top shows nothing with 
a lot of memory, named has 38 M and one other task has 12 M and nothing 
else is over 10 M. 

Is there something I can run that might tell me who's got all the 
memory/swap?

Is there a way to hide a process that top won't display?

Thanks,
Jim.