Geforce FX5500 Vs. Radeon 9550 (+ lots of questions)

I am a major The Sims 2 fan, but I just can't expierience it fully on
my PC:

Pentium 4 2.6ghz
256mb RAM
32mb integrated graphics

As far as I understand, the processor is fine, it's the other two
that's causing the problem. I've just ordered another 512mb of RAM so
that's that sorted.

However, I still need a new video card.

Living in Ireland, and not having a credit card, my options are
limited.

So basically I have two options:


Radeon 9550

and


Geforce FX5500

I have a few questions:

1.) I have a fair idea how to install memory, is a graphics card more
complicated in any way?

2.) I have a 4X AGP slot, will these cards work?

3.) Will I be able to play The Sims 2 decently with 756mb of RAM
aswel?

4.) What sort of power supply would I need?