make hover images load on website before hovering

[unwashed potato!]

for my navigatin menu i have a normal image and then when someone hovers over it it loads another image. all good but the only problem is that when you first go on the website and hover over the image for the first time i a while it has to load the image which causes a blank space with no image for less then a second, which looks terrible.

anyway to get it to load the hover images before you actually hover on them?

thanks