To be fair let's think about the increases in HD size over the years.
Year - Top of the Line HD - Windows Version - Windows consumes - % used for Windows
1995 - 2GB - Windows 95 - 150MB - 8%
1998 - 10GB - Windows 98 - 250MB - 4%
1999 - 30GB - Windows 2000 - 800MB - 3%
2001 - 80GB - Windows XP - 1400MB - 2%
So yes disk usage for Windows has roughly doubled every 2 years, but HD space has doubled every 14-16 months. My newest HD is a 200GB and my using 1.4 out of 200 to install windows doesnt feel like much at all. Remember that the biggest differance in disk usage between 2000 and XP is System Restore. Like KraziKid said, why not just spend the $10-$15 and get yourself a 20GB HD on Ebay.
-Spy