For reason's beyond the scope of this post I needed to uninstall a 64 bit version of SQL server standard edition (Including Integration Services ) and re-install the 32 bit SQL Server standard edition.

The uninstall seemed to complete successfully so I went on my merry way and I attempted the re-install of the 32 bit version:

The database engine installed perfectly well but when the installation got to Integration services, it  failed with the following error:

Failed to install and configure assemblies E:\Program Files (x86)\Microsoft SQL Server (x86)\90\DTS\Tasks\Microsoft.SqlServer.MSMQTask.dll in the COM+ catalog. Error: -2146233087
Error message: Unknown error 0x80131501
Error description: One or more of the components being installed are already registered as 64 bit components in the target application. You must install the 32 bit versions of the components being installed in a different COM+ application, or delete the existing 64 bit versions of the components being installed from the target COM+ application prior to attempting install of the 32 bit versions. COM+ applications cannot contain bit neutral components.

After a few expletives and a google search I found this post on the MSDN forums, I had got the exact same error as the OP in this post:

http://social.msdn.microsoft.com/Forums/en-US/sqlsetupandupgrade/thread/a433b076-5b6f-48e0-9927-76f7f5a1e0ab

so I followed the proposed answer by Ekrem Onsoy:

- Open: Start\Programs\Administrative Tools\Components Services,
- Expand "Component Services" -> "My Computer" -> "COM+ Applications",
- You'll see "Microsoft.SqlServer.MSMQTask" component. Right click on it and Delete it.
- If that dialog box is open which poped up during SQL Server Setup then click Retry, otherwise start over and this problem will be gone.

My next attempt at a reinstall resulted in a different error:

"Failed to install and configure assemblies E:\Program Files (x86)\Microsoft SQL Server (x86)\90\DTS\Tasks\Microsoft.SqlServer.MSMQTask.dll in the COM+ catalog. Error: -2146233087
Error message: Unknown error 0x80131501
Error description: FATAL: Could not find component 'Microsoft.SqlServer.Dts.Tasks.MessageQueueTask.ServCompMQTask' we just installed."

All other components including the database engine seem to install correctly.

I tried the proposed fix above and the component was not there. I rebooted the machine and started again and the install completed successfully.