VGA is analog, hdmi and dvi are digital, so you'd need a fancy(expensive) analog vga to digital dvi(or hdmi if you can find it) converter box, and last time I checked they were like $300.
(okay, now they're just over $200).
http://www.infinitecables.com/pop/ct_cp-261h.htm
Side note: DVI has three variants, DVI-I, DVI-D, and DVI-A.
DVI-I is what most pc graphics cards have, and it supports both digital and analog output. Hence why you can put a dvi to vga adapter and have it output analog.
DVI-D is what a lot of tvs and monitors have, and it's a all digital signal.
DVI-A is all analog with a dvi connector, I've never acutally seen this used though.
So you can go from dvi-i to analog, but going from analog to digital requires a converter.
Edit: If you have an agp or pci-e slot you could buy a new video card with hdmi out for about half the price of a converter box.
http://www.newegg.com/Product/Product.asp?Item=N82E16814102032
http://www.newegg.com/Product/Product.asp?Item=N82E16814102069