continuous hard disk access - slowing down my machine

Question

I find from the hard disk access LED on the front of my machine that the hard disk is being accessed more often and probably because of that, my machine is quite slow. The machine becomes unresponsive even when the load as seen from w command is around 1 or so.

My desktop is optiplex 360 dell machine running Ubuntu 10.04.

EDIT

output of $free

           total       used       free     shared    buffers     cached
Mem:       3983388    3414860     568528          0     205640     315048
-/+ buffers/cache:    2894172    1089216
Swap:      3999736    1035244    2964492

output of $vmstat

    procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
1  2 1035420 564228 210144 312896   22    8   325   343   18   14  3  3 84 10

My questions are:

1. How to quantify hard disk access and how to see if it is more than "normal" ?
2. If it is more than normal, what are my solutions ?

thanks

suresh