Clearing swap and hibernation files properly
Two neglected open books
The reason why I recommend using a swap file with the same initial and maximum size is simple: by default, Windows will allow the file to grow as needed, and this means that data traces will be scattered all over your disk. As the file shrinks, some data will no longer be allocated to pagefile.sys, but it will still be there on your disk. Keeping the swap file a fixed size keeps its data allocated, making it easier to clean. It's also good from a performance point of view, as disk defragmenting lasts longer when you haven't got fragments of pagefile.sys interspersed with other fragments all over the place.
So, what size should you choose? If you are short of RAM, try 1.5 to 2.0 times the amount of RAM you have. But if you've got 1GB or more of RAM, you'll rarely need more than a 1GB swap file on a home system.
Paying for convenience
Alternatively, you can use BCWipe, for which you must pay, which will eliminate the unused portion of the swap file, but not the current data in it. However, it can encrypt the swap file, if you like, so that its data can't be read. Read the help files carefully, and follow the recommendations. I will outline them briefly, but you need to get this right. First, choose a specific size for your swap file as described previously. Next, initialise the BCWipe CryptoSwap utility. Be sure to choose the option "Initialise swap file with random data when Windows starts". Now reboot. Next, do a disk wipe including file slack, disk free space, and the swap file. This will remove any leftover swap-file data traces, leaving only encrypted data in the file.
This utility encrypts and decrypts on the fly, so there is obviously going to be some performance overhead. For that reason, not everyone is going to like this method, but it is far more convenient than the manual method outlined above. You do it once, and from then all you need to wipe are file slack and free space, and of course, individual files as appropriate.
Good news for Tuxers
On a Linux system, the swap file is a disk partition and it can be wiped easily with a free tool that I created called LinuxWipeTools. This is a collection of simple Bash scripts that will allow you to wipe your disk in three modes: the swap partition alone, free space only, or an entire disk. The one you want is called WipeSwap.sh. Launch it from a root shell, and it will automatically detect your swap device, wipe it securely, and re-create it for you. You can run it conveniently in the background while you are using your computer, and there is no need to reboot. You can easily modify it and set it as a cron job, and have a freshly-wiped swap partition every day, if you like, without the slightest bother.