I just thought I would share my experience. I have Dell Inspiron 530 with Q6600 3GB RAM etc. I purchased Arctic Cooler 7 Pro. Will it fit? Yes! Will it be easy? NO! The stock fan screws in, the Arctic cooler comes with those push pin clips. So, you must either, 1. Pull the entire motherboard, and force the glued on bracket off the back of it. or 2. Purchase one of those thermalright bolt through kits for 775 socket, remove the push pins and bolt it in. Which, many have reported cools better than the clips. I also have a 8800GS, and used tape mod to overclock to 3ghz / 1333FSB, PSU is fine, temperatures are fine, stability is fine. Oh, the dell installed micro trend anti-virus was giving me stability problems, not one problem after I removed it.
So, upgraded PSU, unnecessary unless going higher than 9600GT/8800GT. Upgraded case, unnecessary. Even the Arctic Cooler, I was getting high 30s low 40s idle, and no more than 61 Celsius playing lost planet for an hour with the stock fan/heatsink. Its a little warm, but hardly going to cause a meltdown.
Now, I am no pro, this is just my opinion based on what I did.