.Net framework 3.5 无法安装，附解决方法

下载了VS2008,结果在安装时总是失败，检查日志，提示：
[11/22/07,18:04:40] Microsoft .NET Framework 2.0a: [2] Error: Installation failed for component Microsoft .NET Framework 2.0a. MSI returned error code 1603
[11/22/07,18:05:13] WapUI: [2] DepCheck indicates Microsoft .NET Framework 2.0a is not installed.
[11/22/07,18:26:27] Microsoft .NET Framework 2.0a: [2] Error: Installation failed for component Microsoft .NET Framework 2.0a. MSI returned error code 1603
[11/22/07,18:26:57] WapUI: [2] DepCheck indicates Microsoft .NET Framework 2.0a is not installed.
[11/22/07,18:49:56] Microsoft .NET Framework 2.0a: [2] Error: Installation failed for component Microsoft .NET Framework 2.0a. MSI returned error code 1603
[11/22/07,18:50:28] WapUI: [2] DepCheck indicates Microsoft .NET Framework 2.0a is not installed.

在网上反复多次搜索，估计是自己的系统里装了 SQL 2005 SP2,导致 .Net 2.0 SP1 无法安装造成。
最后找到了一个 .Net Frame 清理工具，清理后重新启动，再次安装，成功。

附dotnet清理工具：dotnetfx_cleanup_tool