We can check your PSU for you, if you don't mind opening up your case and just tell us what's written on the side of your PSU.
Or take a pic of it and post :3
Now as Muffin Man said.
4850 > 9800 GT
PCI is a connector type.
The graphics cards will go in the PCI - Express X16 slot though.
PCI Slots are for things like extra USB hubs, older sound cards, older graphics cards, fan slot coolers, and a slew of other useless junk attachments. (IMO)
I'll be glad when motherboards cease including PCI slots and just have PCI-Express slots personally.
Now as for your PCI-E 2.0 question, it's just an update to the old PCI-E bus allowing for twice the bandwidth of PCI-E 1.0 buses.
It won't really matter for you though, as PCI-E 2.0 cards are backwards compatible.
And a 4850 or 9800 GT won't be bottlenecked on the older PCI-E 1.0 connection.
Only very new cards that eat loads of bandwidth really need PCI-E 2.0 X16 and even then the limitations aren't atrocious.
You better overclock your Athlon X2 to at least 3Ghz or I'm going to be disappointed in you.
If you want a great gaming card that your PSU is almost guaranteed to be able to handle
Only uses between 50-60 watts at load, and performs above a 4670 in performance, slightly below a 9600 GT.
It could run WoW with ease and get as many FPS as you could possibly want, and is easier on your wallet than the cards you're looking at.
Also, it doesn't need any PCI-E connectors or anything.
You just slap it in the motherboard slot, and it's good to go.
Also, it's low profile which means it should be relatively quiet and it shouldn't get too hot.