Just thought someone might be interested on this bit:
If you're configuring BAS on BizTalk Server 2004, and you have the Whidbey version of the .NET Framework installed, you might get an error during the configuration wizard similar to this one:
Error encountered while querying virtual server state for URL:
Error Detail: Could not load type 'System.Int32' from assembly 'mscorlib,
Version=1.2.3400.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
To fix it, go to your BizTalk installation folder, and create a new configuration file for ConfigFramework.exe and force it run with v1.1 of the framework:
Then, run ConfigFramework.exe again and you should be able to complete the installation of BAS.