A little-known trick that I do for everyone who tells me that their Windows computer is starting to get slower is to raise the amount of Virtual Memory.
Here are the steps:
Go to Control Panel -> System ->
Advanced. Under the "Performance"
section, press "Settings", then chose
Advanced tab again. The last category
is Virtual Memory, press Change to
change the values.
You will get a list with all your
partitions.
[...]
For the partition where you want to
make virtual memory, chose "Custom
size". You must specify initial and
maximum memory. For the initial size,
put a value equal to your RAM Memory,
and for maximum, twice. This is not a
rule, you can choose what amount you
want as long as your computer works.
If you get the message: "Virtual
Memory Minimum too low", raise the
initial size value.
You'll want to change the amount on your main partition, setting it fairly higher than the current amount.