I dont think I have ever heard of the CPU using 3.3v lines. The CPU doesnt get any direct power from the PS anyways, The CPU voltage regulator is fed 12v from the PS and then the actual voltage of the power the CPU uses is carefully controlled.
3.3v is used by hard drives...in conjuction with the 5.0v, AGP cards, many PCI cards.
If you are seeing a lack of power, spare yourself a lot of problems and buy a new power supply. I think tomshardware does the best powersupply testing/reveiws. Check it out and decide on a new powersupply.
I went with Enermax because of their implementation of ATX 1.3, if that doesnt matter to you....I would suggest an Antec TRU POWER.