configuring screensavers

[yavamoni]

I am probably missing something obvious, but... How can I configure the "screensaver theme" I choose?

I can't find a "customize" or something like that option under "Preferences->Screensaver" - I am quite sure there must be options for at least some of the screensavers...? (I am looking for options like what folder to search in the GLSideshow one)

I have just upgraded to Ubuntu 10.04.

Thanks a lot!