I'm using TortoiseSVN and Visual Studio 2008. Is there any way to update my project's assemblyinfo.cs with svn's version in every build?
For example, 1.0.0.[svn's version] -> 1.0.0.12
You could use the SubWCRev tool which comes with TortoiseSVN (also available separately).
Either run it from a command line or use the COM-Object it offers.
The SubWCRev command line tool replaces keywords inside a file with information from your svn working copy. An example is shown in the docs.