Upgrade on PC need help!

Hello,

I wrote this same thread on the PC forum, but that's dead, this one's alive, and I want to make these purchases tonight if I can get my questions answered. I currently own a gateway and want to upgrade it slightly, just to get some more 'oomph' out of it. I have been doing some extensive research on the latest video cards and benchmarks the past few days, and it seems the best card for under 200 is the 8600gts (EVGA). I won't bore you all with my rambling, so I will get right to the questions. Firstly, here are the links to my PC specs and the parts I want to add, respectively;

My CURRENT PC specs; http://support.gateway.com/s/PC/R/1009400/1009400sp2.shtml

GPU; http://www.newegg.com/Product/Product.aspx?Item=N82E16814130086

RAM; http://www.newegg.com/Product/Product.aspx?Item=N82E16820145527

PSU; http://www.newegg.com/Product/Product.aspx?Item=N82E16817153052

Also, a link to an excellent article I found regarding the 8600GT vs GTS, including detailed benchmark graphs;

http://www.guru3d.com/article/Videocards/426/

OK, so now you know my PC specs and what I want to add, so I have a few questions to ask;

1. I am pretty sure, but I just want to triple check (and get a pros opinion) that the GPU, RAM, and PSU will all fit and be compatible with my computer.

2. If I add 2x1GB of RAM, will the current 2x512MB of RAM currently installed work with it, or will I have to remove it?

3. How hard are PSU's to install. I am buying a new one because my current is 300W, and I just want to make sure everything is safe.

4. Do you feel these are good parts, brands, etc? I don't need a high end gaming rig, because I really only use the PC to surf the web, check email, watch TV, and OCCASIONALLY play a game or two. Right now I'm really interested in running Hellgate:London with decent fps and high settings with those added parts. I should be good for that right?

I really think that's it, so basically just gimme your input, lemme know if 100% for sure these 3 parts will fit and be compatible, and if they are good performance (unless you STRONGLY feel I should get another vid card in the same price range, I really find this to have the best performance on every article I read). Also, I only want an 8 series as I want DX10 capability, and don't want to spend the extra 300 for an 8800 so don't mention that lol.

*I would like to make the purchase in the next hour or two, so any immediate help would be awsome. Thanks gamespotters!

look more people would answer your question if you just told us the parts in ur pc

instead, we have to click, press back, click press back.

also, if your going dx10, i suggest the 2600xt 512mb, you will get more 'oomph' than that out of a 8600