BleepingComputer.com: Upgrade Compatiblity Question

I'm upgrading my computer, and can't figure out if the upgrade I'm going to do is going to work in my computer, and how well it will work.

Current setup:
Lenovo J115
AMD Athlon 64 X2 3800+
1GB RAM DDR2 (512MBx2)
ATI Radeon x1050
450W PSU (I think)

And I'm upgrading to:
2GB RAM DDR2 (1GBx2) http://www.newegg.com/Product/Product.aspx...N82E16820231098
ATI Radeon HD 3850 http://www.newegg.com/Product/Product.aspx...N82E16814129102

I assume I'm going to have to upgrade my PSU too, but what should the minimum be?

I looked up that model of computer, and that graphics card should work fine. If you have a good quality 450Watt power supply, I don't think its necessary to get a new one.

About the ram though, You have DDR2 800mhz posted, when it says your computer uses DDR2 533mhz. I think it should be alright, the ram should just clock down to 533mhz speed, the newer DDR2 stuff does that. I'm only concerned about this because one time I put DDR 400mhz ram in my friends computer that also had a DDR 333mhz stick. When I turned the computer on I could smell electronics burning and the computer would not boot properly. It turns out that the slower 333mhz stick that was in there got fried and the slot it was in doesn't work anymore. Hopefully someone else can come along and give you advice on what ram to get.

Power supply calculator
Crucial use their memory adviser to find what's recommended
Mark