Using X programs after su?

Hi, does anybody know how to use X programs after su-ing to another user? It used to be that I could simply enter 'xhost +localhost', and it would work. But in more recent Suse distributions (currently running 9.1), it doesn't work like that anymore. I can get it to work by ssh-ing into localhost with the -X flag, but I don't want the encryption overhead for a local user. Thanks for any help, Claus