Replacing old desktop's video card. ATi Radeon x850 OR Nvidia Gefroce 8440

[maebach]

My old desktop computer's ATi Radeon 9800 All in Wonder died and I'm looking for a cheap replacement. My motherboard is an Asus P4PE, processor is a Pentium 4 and I have 512mb of ram. I'm not too technically savvy so I dont know which to purchase or which one will work. The two alternatives I'm thinking of are:

ATi Radeon X850 256 mb OR the Asus Geforce 8440 128 mb.

My questions are as followed:

1. Which card is better?
2. My ATi 9800's card is an AGP and bother cards I'm profiling are also AGP cards. My ATi card has 3 'slots'/'keys'/'teeth' (I'm not sure how to describe it, but the part of the chip that plugs into the motherboard). So those my ATi has 3 seperate parts to its slot and from looking at pictures of the X850, even though it says it's AGP, for some reason it only has 2 sets of 'slots'. Will this card still work? The Geforce has 3 'slots' so Im comfortable with that.

Mine:
http://i40.tinypic.com/2nrf3f7.jpg

The X850:
http://i42.tinypic.com/bj7qcj.jpg

8440:
http://home.datacomm.ch/charlydog/Pics/Thumbs%20VGA/Asus%20AGP-V8440.jpg


Thanks for the help everyone!

[tesco]

I found this regarding the slots/keys: http://www.playtool.com/pages/agpcompat/agp.html

[MysticRiffs]

Okay, couple of things... Look in between the first two PCI slots, mate, and it should give you the exact model number of the board. The choice are :P4PE; P4PE2-X; P4PE-BP; P4PE-X; P4PE-X/SE; and P4PE-X/TE.
It's important enough that they give them different letters, so we need to double check that.

A lot of people are gonna tell you the x850, hands down. That's because it a better GPU, on spec. :D The problem is though, I'm fairly sure it won't fit your board, as you've already highlighted with you picture. My best advice, based on the limited info, is to do a search with your preferred online vendor for AGP 8x GPUs.

I've also noticed you've posed the exact same questions on different forums, so hit the guys up over at http://www.techpowerup.com/forums/showthread.php?t=185131. They have an AGP enthusiast forum. ;) Hope this helps. :)

EDIT

Forgot to mention... if you're replacing a legacy unit, you absolutely should do yourself a favour and beg, borrow or steal a power supply tester, mate, as it's dollars to donuts that yours is now running under half rated capacity, and that mobo combined with most GPUs is gonna have about 350W headroom.