Quiet PC Owners... PLEASE RESPOND!

OK, I just bought a 4500 Diminsion a few months ago. I have upgraded to a 80 Gb Seagate Barracuda hard drive, with a Smart Drive 2002 hard drive enclosure. My noisy GeForce 4200 Ti GPU fan has peen replaced with a massive Zalman GPU heatsink. I got all this from siliconacoustics.com, and my hard drive and graphics card are now virtually silent. After that, I noticed my case and PSU fan noise. Subtle, but I need COMPLETE silence. Now, I would like to further silence my system by getting a 92mm Panaflo case fan and Nexus NX-3000 PSU, as they are rated the quietest by many PC enthusiast reviews. But I have found since that Dell PSUs are proprietary. On further reading though, some people say that you CAN use ATX PSUs on Dells. Read here: http://forums.us.dell.com/supportforums/board/message?board.id=dim_other&message.id=137241. So what I have so far is this; my Dell PC can take standard ATX PSUs, without special adapters or connectors, but the case itself isn't designed to take ATX, so all I have to do is cut a hole in the back so the power switch and cord can fit, right? OK, second question, I have noticed that my case fan isn't screwed in, rather it uses rubber nubs to hold it in place. Is it OK to just pull it out? Or would I have to cut it and get new rubber nubs? Thank you all for your input, sorry about the long post and all, I just wanted to get specific answers. Happy new years!