I was going to toss out some Pentium 4 class power supplies which are 20 pin type and a friend SUGGESTED I save them and USE them with a cheap 20 to 24 pin adapter which would make the power supply able to work with a modern 24 pin board. Anyone used this type of adapter to say whether it would work or not? I have some better brand P4 power supplies that are like 400 watts etc that I could use if its an ok adaption.

Concern I have with 20 to 24 pin adaption is that, while I haven't checked the pin differences to see what voltages are on the additional 4 PINS in the 24, it appears that they are feeding 4 pins in a Y configuration off of other pins and, if a pin is suppose to have say a dedicated 1 AMP and its now SPLIT between 2 pins, there is additional draw that might weigh down that leg of the power supply.

http://www.ebay.com/itm/like/291407955450?lpid=82&chn=psThe additional draw is exactly why it adds the extra 4 pins. the 4 pins add a  12v (Yellow) a 5v (Red) a 3.3v(Orange) and an additional Ground pin (Black). The adapters as you've noted simply split those from existing pins.

Of course, whether those pins are separate rails are something I'm not privvy to and probably depends on the PSU itself. Generally more recent power supplies that were made to support the 24-pin connector have increased amperage ratings on the affected rails to account for the increased draw. Older, 20-pin supplies will not have this.