If you hard drive light is blinking non stop, it might be a good idea to investigate. There are two ways to peek into hard drive activity in Windows. Using perfmon or task manager. Task manager can be used to track which process is using the disk aggressively and perfmon can be used to track the metrics related to disk activity like disk queue, Disk reads/sec, Disk Transfer/sec, %Idle Time etc.
Task Manager: Open the task manager by three finger salute (press ctrl-alt-delete together). Select the "Processes" tab. In the menu select "View -> Select Columns". Select I/O Read Bytes, I/O Write Bytes and I/O Other Bytes. (In Vista it is I/O Read, I/O Writes, I/O Others). This will show you the cumulative values, which means that the processes which are long running may have accumulated a lot of I/O read or write bytes. If you want to find the culprit of unusual disk activity you need to find the process whose I/O numbers are increasing fast.
Perfmon: Open perfmon by typing perfmon in Start->Run. Right click on the pane below the graph. Choose "Add Counters". In that window choose "Physical Disk" for Performance Object. Select the counters you want monitored like Disk reads/sec, Disk Transfer/sec, %Idle Time etc. You can select more than one at a time by holding down Ctrl key while clicking. The normal values for these counters depend on your system. So to have something to compare with it is advisable to save the values of these counters when the system is behaving normally. To save logs