I use another host that only uses windows 2003 and every thing works fine. Perhaps Windows is not The Problem( don't forget that Windows 2003 Server was 3 years in beta testing, including the Microsoft.com web site, that has hundreds of servers, and it works very well.)
There are known issues (such as jet/oledb driver issues with Windows 2003) that Microsoft has still not addressed
We have worked with both operating systems extensively and feel that Windows 2000 is a more stable environment to offer hosting to our customers at the moment. Windows 2000 has been time-tested with 5 service packs and hundreds of patches been released since win2000 hit the market.
Win2003 has been released only recently and there are flaws that should eventually be addressed through its first service pack. We are not ruling out Windowsw 2003 for the future, it is the future but we are not comfortable with introducing more win2003 servers at the moment