'... any reason for this?' - yes, you require a 'Quartz' video capable Mac; or, must replace the video card (if a Power Mac) with one that is.
If you double click on a '.qtz' file and the 'Unsupported configuration' alert box appears, you have confirmed the statement above.
'... like they are two different formats!? is this right?' - that is correct.
'why would they do that!' - why not e-Mail Apple?
'i can't use any of the resexcellence screensavers.' - yes you can, the non-Quartz ones.
'i put the screen saver in both "screen saver" Folders located in users and system folder.' - you should place 'screen saver' files in either a '~/Library/ScreenSavers/' folder (for access by only that user) or the '/Library/Screen Savers/' folder (for access by all users). But, never in the '/System/Library/Screen Savers/' folder. To do such (the latter), would require entering an Administrator's password. That result alone should be enough for one to reconsider the action they are about to make.
'... its all in some unreadable font' - remove the font.
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When posting: include your model Mac and its OS version ('Tiger' is up to version 10.4.4 [with 10.4.5 in process]), the specific file(s), font(s), etc., you downloaded / installed - and their respective URL(s).