I have just done a re-install of Vista Home Premium (from OEM disk) on my desktop.
I formatted the drive during install so it was empty when the Vista install started.
I have done the install, and downloaded ALL the Windows updates (this was loads of files, and hundreds of megabytes, and included SP1, SP2 and NetFramework which were all large). It did this in five or six goes, not all at once.
I have not installed ANY other programs (except flash and shockwave and quicktime in the web browser).
I now find my software is taking up 20Gb of my disk.
My Windows folder alone is 17Gb (18,089,560,900) and 85,926 files and 18,364 folders.
How big are other peoples Windows folder?
(Go into Computer, double click on C drive, right click on the Windows folder, and select Properties from the menu. Give it a few minutes as it takes time to add up all the files and folders. It can stop and start a few times so wait till it has finished).