Your RAM upgrade for one stick will probably cost around $200. RDRAM = EXPENSIVE! Also, with only $400, you can't do much video card/RDRAM wise, but that PSU you can upgrade to a decent 350W-400W for ~$70.
Newegg.com
Also check out Toms Hardware:
Which is found here
And finally:
Pricewatch
EDIT: Most any new video card will use a larger PSU. Also for the RAM issue, if it is gaming, 512 is usually fine, so the video card alone should fix it. I just spent $500 on this card:
Ati Radeon X800 XT
Very expensive, but also will last you a long time.
Newegg.com
Also check out Toms Hardware:
Which is found here
And finally:
Pricewatch
EDIT: Most any new video card will use a larger PSU. Also for the RAM issue, if it is gaming, 512 is usually fine, so the video card alone should fix it. I just spent $500 on this card:
Ati Radeon X800 XT
Very expensive, but also will last you a long time.
WWBBD?