EPS Files Do Not Open Correctly

I think the underlying cause of the problem is the change Apple has made in how Launch Services is identifying these files in Tiger.

An Illustrator EPS file most likely has a creator code of 'ART5', a file type of 'EPSF', and a filename extension of ".eps". A Photoshop EPS file has a creator code of '8***', a file type of 'EPSF' (same as an Illy EPS), and a filename extension of ".eps" (again, same as an Illy EPS).

Prior to OS X 10.4, Launch Services would consider an Illustrator EPS file to be different from a Photoshop EPS file because of the different creator codes on the file. (While we know that they are different based on the type of data they contain (i.e. vector vs. raster), Launch Services doesn't really know anything about the content of the files; it only looks at the file properties to make its decisions). Since they were different, you could choose to have one open in Illustrator and the other open in Photoshop.

In OS X 10.4, Apple changed some things around. Prior to 10.4, a combination of a file's creator code, file type, and filename extension were mapped to a particular application that would open it. In 10.4, the file's creator code, file type, and filename extension aren't mapped directly to an application, but to an intermediary called a "Uniform Type Identifier" (UTI). It's the UTI then that is mapped to an application that will open it. The UTI for an EPS file is the string "com.adobe.encapsulated- postscript". Launch Services doesn't really distinguish between an Illustrator "com.adobe.encapsulated- postscript" file or a Photoshop "com.adobe.encapsulated- postscript" file. So, what happens is that both an Illustrator EPS file (creator code 'ART5', file type 'EPSF', filename extension ".eps") and a Photoshop EPS file (creator code '8***', file type 'EPSF', filename extension ".eps") are mapped to the same UTI type, "com.adobe.encapsulated- postscript", which itself can be globally mapped to only one application. In other words, globally either Illustrator or Photoshop, but not both. While not ideal, files do support a per-file preference setting. So if you have a global setting to open eps files in Illustrator then by default double-clicking on will, well, open them in Illustrator. If you have a Photoshop EPS file and would like to open it in Photoshop, you could use the Get Info window to choose Photoshop instead -- just don't click the Change All button. That file, from then on, should always open in Photoshop when you double click on it. (That "user override" preference is saved in the resource fork of the file so it should stay with it).

The switch to UTI's has helped simplify things quite a bit, but this is really one instance where it's counterproductive. You might want to send feedback to Apple about it.

Hope this helps....

Dual 2.7GHz PowerPC G5 w/ 2.5 GB RAM; 17" MacBook Pro w/ 2 GB RAM - Mac OS X (10.4.6)

another option, as a temporary, but not necessarily future proof solution would be to edit the Info.plist files for both Photoshop and Illustrator to include UTI definitions. you could put a different UTI in each one, and differentiate between them for opening purposes.

As a reference you'll want to look at apple's UTI page:
http://developer.apple.com/documentation/Carbon/Conceptual/understandingutis/understand_utis_conc/chapter_2_section_4.html#//appleref/doc/uid/TP40001319-CH202-BCGFBBIA
as well as at the info.plist for an application that already has some UTI definitions (ex Safari)

The info.plist file for an application can be found by control-clicking on the application and choosing 'show package contents' in the resulting context menu. then open the 'contents' directory to see the Info.plist file. Most of them are plain text files, but one or two are binary files that you'll need PlistEditor (included in apple's developer tools) to open.

Good luck!