Sufficient Memory? Cannot Install Programs

I am currently not able to UPDATE or Install any programs.

I get an error: "Couldn't install on USB storage or SD card".

I think the problem may be related to the shrinking amount of available internal memory on the phone:

Memory Info:
Internal: 28 MB Available, out of 225.8MB Total
SD Card (32GB): 21.7GB Available

Can you tell me what files can be safely deleted from the phone's internal memory to clear this trouble up?
Example, I notice that there are several files, which appear to be archived download/install files. Can these be deleted?
/PROC/ (any of the thousands of subfolders here??)



/sdcard/download/ (any of the download files? ie: downloadfile-31, etc.)

I have deleted several applications, but this hasn't seemed to correct the problem.

Any Ideas?
Also, know of any programs that clean up residue from uninstalled programs, etc. (if I were able to install it :-( )?

Thanks,
JT