768mb = 1/3 of the drive? Must be a small drive :)
If you haven't altered the swap file settings manually, Windows will resize it as it needs to. Some people recommend moving it to a drive that doesn't have the OS on it; or to another partition. Some people recommend setting it manually, to a fixed size, so Windows isn't resizing it all the time and slowing things down.
I have two HDDs so have a fixed size page file of 1024mb on the drive that doesn't contain the OS. I have 512mb of RAM.