Thank you for the fast reply! No,the small previews,while always a bit darker,were always close enough to the final image.These problems just appeared (even in saved scenes that were fine before) ,and the final render was really washed out compared to the previews.I went out and bought a new GeForce card today and all is back to normal.I experienced a rare BSOD with WinXP last night,and when I posted the error report to MicroSoft,it told me a hardware problem that never appeared in my Device Manager.I'm thinking that the old card was going out.

I will most definitely check out your tutorial! Many thanks!