If you are getting Internal Server Error 500 on even mt-check.cgi, it is likely that one, or more, of the most common causes of that on DreamHost is involved:
1) Make sure all your .cgi files are transferred using ASCII mode of FTP
2) Make sure all your .cgi files are set to 755 permissions (even if instructions say 777 or 775)
3) If you have edited your files with a windows or MAC OS9x editor, make sure that you account for the different line endings in use, which any one of the following methods will accomplish:
a) Save the file with *nix line endings if your editor allows it
b) Open and re-save the file on the server using a *nix editor
c) use a utility on your computer or the in the shell to do the conversion. (dos2unix, fromdos, etc)
It also might help to inspect your error log to see what additional information is provided about the error.