It seems SVN's "patch" functionality is not exactly what I want. What I really want is to create a diff of files between revisions. So, I'd choose rev1 and rev 2 and end up with a folder containing all files that were changed or added between those revisions.
Can this be done with Tortoise SVN or plain-old svn?
From the command line you could do this as follows.
Create a patch in your Home folder that contains all the changes between revision 123 and 124 from all the changed files in the folder "my_project":
svn diff -r123:124 path/to/my_project > ~/my_project_changes_123_124.patch
Create a patch in your Home folder that contains all the changes between revision 123 and 124 from only one file, name "my_project.php":
svn diff -r123:124 path/to/my_project/my_project.php > ~/my_project_changes_123_124.patch