Have you heard about Google Art Project? Using it's Street View Technology, Google allows you to tour 17 museums on your computer screen. Using Google's cameras, you navigate your way through rooms and galleries, clicking on paintings marked with a (+) for a closer look. I've tried it out, and though it's a bit of a wobbly, woozy, uneven experience at times, it's impressive - and as close to most of these places as I will ever get.
Ben Davis did an editorial piece on the project over at ARTINFO, And I found Roberta Smith's piece in the NY Times to be a fascinating look at some of the museums and artworks featured -especially the images Google has made available in super-high resolution - which allows you a nose-to-canvas view of some of the world's great masterpieces, such as Chris Ofili's No Woman No Cry in the Tate. Clicking on "View in the Dark" will allow you to see the glow-in-the-dark message hidden in the painting. (Not to mention the balls of elephant dung that serve as the painting's "feet".)
Google has a couple of tutorials to get you started - here's one of them. Or, just jump in and start exploring. You may be gone awhile.