Good PSU for HD 4850 ?

Hi, I've got a Inspiron 530, with a 300W PSU (acbel) and the Core 2 Duo E45000 (2,2Ghz), a CD/DVD reader/writer, external card reader and I added a BD reader. Since the GPU is an integrated G33, I though I should use the pci-e slot to upgradre a little and get a real graphics card. I'm not a huge gamer, but I like to play good game when I got the time. My display is a 23" Samsung 2333HD (1900*1080).

I though about getting this card :
http://www.newegg.ca/Product/Product.aspx?Item=N82E1681...
(HD 4850)

and I know I'll have to upgrade the PSU so I tough about getting this one:
http://www.newegg.ca/Product/Product.aspx?Item=N82E1681...

I know it's some what cheap for a PSU, but this computer is really just for 3 more years, after that I'll just connect it to a TV screen and use it for emulation/ multimedia / BD reader/exceptional home LAN parties(when someone just forget his computer).. So, what do you think? I looked at http://www.extreme.outervision.com/PSUEngine , and it's telling me a 400W PSU would be enough... but I tough I'd double check here