Buy quality -- and by consensus on most forums avoid Qtec
Take anti static precautions. Have some decent tools available when you are disconnecting the power supplies to your components. It is amazing how stiff some connectors like molex and ide can become. Try and pill at 180 degees dead striaght but expect to have to do a bit of prising and rocking.
Have just had a good look at the old PSU - Dan 250 It has tons of cables coming out of it. Will the new one have a compatible selection od cables. I had inagened that I would plug in to it directly with my cables - hope springs eternal. Have heard Q Tex is good.