I think 230W is some what gutless, especially it it's possible to add an ATA 100 or 133 PCI IDE card (well, it's a bit tight with the video card, even though it will be on the bottom PCI slot and not the stub...I could add another optical drive and 1-2 more IDE hard drives almost immediately...
You rigged a small CPU fan to the video card, might one of my PVI card vent fans do the trick?
Which side is that fan on anyway?
I wouldn't go adding more drives to the Dell as there isn't really room for more. There is a second bay next to the primary drive, if you purchase one of the dell drive caddys. They want about $5 or so on ebay. You will need a sata cable to reach down there too, but with a 500GB Primary drive you shouldn't really need to add any more internal drives. If you really need more storage, and in that case I would buy a 1tb drive and clone the 500gb drive over to it.
If you want to pull the fan off off the graphics card, it is kind of a toss up on the 6600, it may or may not run ok without a fan. A vent fan may work fine for it.
If you have a small fan like an 80mm you could piggy back it on the the side of the old power supply sure, or you could open up the power supply and put a new fan it. The fan should go the direction of the arrows on it. Power supplys fans always pull air through the power supply and send it out the back of the power supply, The fans can either be on the front of the back or even the bottom of the power supply. I still think the 230w psu will work fine even with three or four drives in the computer you have it in. I ran specs on the Dell 380 you have an under a full load it would only draw 145 watts, with probably 70 or 80 from the graphics card. A P4 should draw anymore then a quad core and the 6600 should draw that much juice either.