As Microsoft is working on the latest update for Windows Vista, also known as Service Pack 1 or SP1, news has it that it has been leaked on to the internet. Vista SP1 is supposed to be released in Feb and it seems just the right time for Microsoft to label the latest builds as RTM or Release to Manufacturing.
Microsoft is just about to release it to the partners and may be someone from the developers was naughty to release it. Or may it was someone from the partners. Anyway, the leak is some kind of a standalone executable and has the build 6001.18000.080126-2040. Another leak has it as 080118_1840, but its a pretty early timestamp (18-01-2008) which suggests that its a fake. These builds are probably escrow and candidate for the final RTM.
If you don’t have patience to wait till release then go ahead!! But it may screw up your OS also I am not sure about this package nay way try it with your own risk
source:winvista