memory usage

[Charles Malespin]

Hi all, I am running hoary on a Dell desktop with 1 Gb ram.  If I leave
my computer on for a day or so, the memory usage just keeps going up and
up, even if I am not running anything.  At most I will have firefox,
Evo, and some music playing, but it will still show 88-90% memory usage.
27-30% will be cached.  Is there some way to clean this up and monitor
what is causing the rise in mem usage?  Here is what my top looks
like....
 22:27:21 up 1 day,  9:49,  2 users,  load average: 0.18, 0.18, 0.09
Tasks:  85 total,   1 running,  83 sleeping,   0 stopped,   1 zombie
Cpu(s): 13.6% us,  1.3% sy,  0.0% ni, 85.0% id,  0.0% wa,  0.0% hi,
0.0% si
Mem:   1035076k total,   915692k used,   119384k free,   103184k buffers
Swap:  2650684k total,        0k used,  2650684k free,   302376k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 6192 root      16   0  187m  55m  10m S  7.7  5.5  26:47.57 Xorg
 7545 malespin  15   0  179m 169m  17m S  2.7 16.8  56:07.42 python
 8071 malespin  15   0 30568  12m 8388 S  2.3  1.3   1:16.77
gnome-terminal
 7452 malespin  15   0 13224 7792 6132 S  0.3  0.8   0:02.05 metacity
 7458 malespin  15   0 39840  17m 9.8m S  0.3  1.8   0:02.09 nautilus
 7497 malespin  15   0 18252  10m 8012 S  0.3  1.0   0:31.46 wnck-applet
 2997 malespin  15   0 50584  16m 8516 S  0.3  1.6   0:02.55
btdownloadgui
    1 root      16   0  1552  508  444 S  0.0  0.0   0:00.55 init
    2 root      34  19     0    0    0 S  0.0  0.0   0:00.00 ksoftirqd/0
    3 root       5 -10     0    0    0 S  0.0  0.0   0:00.00 events/0
    4 root       7 -10     0    0    0 S  0.0  0.0   0:00.00 khelper
   16 root      15 -10     0    0    0 S  0.0  0.0   0:00.00 kacpid
   95 root       5 -10     0    0    0 S  0.0  0.0   0:00.24 kblockd/0
  129 root      15   0     0    0    0 S  0.0  0.0   0:00.00 pdflush
  130 root      15   0     0    0    0 S  0.0  0.0   0:00.01 pdflush
  132 root       6 -10     0    0    0 S  0.0  0.0   0:00.00 aio/0
  131 root      22   0     0    0    0 S  0.0  0.0   0:00.00 kswapd0


I dont see how I can be using that much memory with 1 Gb available.  
Thanks, 
Charles