20-Pin power worth a shot without new PSU?

Alright, I'm building a friend a computer...

I have an XG Sidewinder case (like in the value PC guide), with a 400W PSU. My Mobo is an EPOX EP-9NPAJ with an A64 3000+, so I have a 20-pin PSU and 24-pin mobo. Now I've read a bunch about it but I'm still stuck... I checked the manual too, and it doesn't say either way... it just says that the 24-pin and the 4-pin have to be used simultaneously. I'm using an IDE hard drive, integrated sound... and my PCIX X800 Radeon has a 4 pin power connector at the top. Do i NEED to use that? Especially if I try to use a 20-pin on a 24 pin mobo? Worst part is, the vidcard or PSU didn't come with an adapter to power that 4 pin connector. Will the extra +12V 4-pin Power connector be enough to power everything? If i need a new PSU it's cutting into my profits!!! thanks for the help... and if this is the wrong forum, lemme know

-D

Probably would have been better under power supply section, but nonetheless. There are adapters you can get for relatively cheap that will convert a 20-pin into a 24-pin.

I know how to plug the 20 into the 24. My question was whether the vidcard would get enough juice. Those last four pins on the main power connector are power to the PCI express slot. And if I don't get additional power to the card using that extra connector it has [Link --look at the top right corner of the card], I don't think it will be stable. Am I right here?

That's why you buy the adapter.

my +12V rail has 17Amps, you think when the two 12V's are split that it's still enough for the x800?

At peak consumption, x800's run at ~93 watts (using data gathered from Tom's Hardware.) Your 12V rail is rated for 17A, which means your max wattage on 12V should be just above 200W. Unless you are using a rather power hungry setup with numerous drives or major overclocking, it should still be sufficient.

What kind of PSU is it, exactly?

An MGE 400W. Someone told me that they're pretty good, anyone else heard of them?