I bought New vegas from Game yesterday, happily.
But when i tried to install it, my the installer told me over and over that there are no free memory, even though i have over 30GB left.
Anyone who have any idea how to solve this?

First, let's correct a misconception, shall we? Memory is far different than storage. Memory is RAM.

Second, it is always wisest to run a defragmentation utility on hard drives every so often, to make certain that storage remains available in large, contiguous blocks, rather than scattered small fragments. Have you done that recently?

oh... didn't think of that...

Well, i cant say i have done that in a while, like... never, so yeah, thats proborbly a good idea. Will do that as soon as i get to the computer in question

Heheh...
And with fantastic drives like WD Caviar Black costing only $50 bucks, ideally you would have more than 30GB free space.
Be aware, you should always keep 10% free space.
In other words, when your harddisk hits 90% it's 'full'...
Regards