TortoiseSVN The coolest Interface to (Sub)Version Control

You can install TortoiseSVN for just one user. But you need at least the privileges to write to the HKLM registry keys. If you don't have those permissions, then you can't install it.

Of course, you can only do this if you already have the MFC and CRT libraries version 8 installed on your system. To install these, you require Admin privileges.
You can get those libraries from the Microsoft website if you really require that TortoiseSVN is only installed for one user.

If you simply want to hide the context menu's in the explorer for certain users, you can use a feature new for version 1.5.x:
Allow disabling of explorer context menu entries.