help regarding redirecting with .htaccess

[arpan.rnc]

hi people ,
i want to know is it possible to redirect a user who is on one of my site at a particular directory and/or page to the same directory and/or page on another site with the same directory structure via the 500 errorDocument ?
like suppose he is on xyz.com/mp3/index.php?u=something and there occurs a server overload ,how can i redirect him to pqr.com/mp3/index.php?u=something using the errorDocument 500 of .htaccess ?
i mean to say how can i get his current location in .htaccess ?
we can easily redirect to another site.but how can we redirect to the same page in the other site, that he is on currently ?

thanx in advance.

[subzero]

More likely 500 handles that overload and if you wish to limit users then php code it ...

[arpan.rnc]

i don't wanna limit users , just redirect them to the same page(their current page) on another site .
i waana know how can i do that ?