I'm able to give files 255 character names from Finder using 10.8 and an HFS+ volume.
HFS+ (which was introduced in Mac OS 8) should allow 255 character names, but it's not clear if HFS was limited to 31 or 255 characters. http://en.wikipedia.org/wiki/Hierarchical_File_System says that the maximum length was 31 characters, but also that the limit was only imposed by Finder:
Files were referenced with unique file IDs rather than file names, and file names could be 255 characters long (although the Finder only supported a maximum of 31 characters).
In January 1998, Apple released Mac OS 8.1 with HFS Plus, which included support for 255 character file names; however, Finder continued to limit names to 31 characters until Mac OS X.
It's not clear if the limit was removed in 10.0 or a later version of OS X.
The startup drives of new Macs should be formatted as Mac OS Extended (Journaled) (journaled HFS+) by default. If your drive is formatted as Mac OS (HFS), you could try try reformatting it, but it requires deleting all files and restoring them from a backup.