As promised I've published the code and instructions to my previous post...
Go and have a look on CodeProject:

Workaround: svn:externals with a space in the directory name:
TSVN Post-Update hook utility for using svn:externals with a space in the directory name
http://www.codeproject.com/KB/files/Percent20toSpace.aspx

Please let me know what you think.

While setting up my development environment for various BlogEngine.NET sites, I ran into the problem that when setting svn:externals: One cannot have spaces in the directory name or the external url with TortoiseSVN.
For example: User controls svn://host/User controls
According to a message in the TSVN mailing list, the trick is to replace the space with "%20", like this: User%20controls svn://host/User%20controls Now being able to add the external, there is a new problem:
When I put the "%20" in the name, I get a directory with the characters "%20" in the name. I could have just used an underscore, but the there are references to the "User controls" directory in the project and for future compatibility I didn't want to deviate from the original structure.

To overcome this I've created a tiny console application to rename the directory when the TSVN Post-Update Hook is fired. I will post the source in the next edition of this saga.