Installing TortoiseSVN for specific users on Citrix XenApp
Two options come to mind:
Set permissions on the directories and registry keys created during the TortoiseSVN install in such a way that users that should not see TortoiseSVN's shell extension do not have read access.
Replace the physical XenApp installation with two virtual XenApp servers on the existing hardware. Install TortoiseSVN on only one of them.