Little help with mod_rewrite

Hi!
I made apache config with few VirtualHost configurations (with loaded
mod_rewrite of course).
I tried use mod_rewrite for one of it but I gets bad request error (400).
Are there any special rules for using mod_rewrite with vritual hosts? (rules
for mod_rewrite works fine on another apache serwer)
(system gentoo, kernel 2.6.14, apache )

Please help!
gx