I have a temporary file that Photoshop 5.5 (PC) created, but I didn't
get to save the image.  The temporary file looks to be just the right
size, but I can't open it directly, and changing the file extension
doesn't work either.  How can I get photoshop to recognize it as a
temporary file, and open it again?

Absterge,

Unfortunately it seems to be impossible to recover a Photoshop tmp
file according to this posting at the Adobe Photoshop Forum:

Topic - Recovering a "tmp" file in photoshop

"While working on a PSD. The file encountered an error while saving,
deleting my psd and making it into a tmp. I am having trouble opening
the tmp format, even if I change the file extension to psd. I get an
error message. Any thoughts would be greatly appreciated."

"Nope that tmp file isn't your file. It's photoshops scratch disk.
Used for a thousand things. You can't get anything out of it. You need
to recreate the original from scratch."

http://www.adobeforums.com/cgi-bin/webx?50@181.xVFIaGNcuFp.6@.1de61135

"No way you can open a tmp file"
http://www.adobeforums.com/cgi-bin/webx?50@181.xVFIaGNcuFp.6@.1de660bd

--Bobbie7-ga