Tech answer:
First of all, your PC is grounded by the power. I've heard of REALLY old houses that have some power problems (100 years old?). But any modern place has a properly grounded AC system.
Whichever card you get, buy one that blows the hot air out the REAR of the case and NOT inside the case.
Ensure proper air flow inside the case. This can usually be accomplished by one or two 120mm case fans (just get LOW FLOW which is not loud). Your case fans should NOT be variable. Get ones that run at a constant, low rate (say 1000RPM). The noise (dB) also depends on the Quality of the fan. Again you are concerned with:
1) Noise/dB
2) Constant (not variable) fan speed of about 1000RPM
3) Quality (comments I guess)
Which graphics card?
Here are the factors which affect the card you buy.
1) CPU (can limit the usage of the graphics card. For example, an AMD/ATI HD4770 should not be used with anything lower than an AMD X2-4800+. In this pairing, some games will be CPU limited and some will be GPU limited which represents a good balance.)
2) VRAM? (1GB of VRAM on a 9800GT is stupid. It's a marketing thing. You can't use more than 512MB. Generally you need a fast CPU, high-end GPU of at least HD4870 at a high resolution of 1920x1080 or greater to justify more VRAM. Otherwise it's just consuming power.)
3) Cost vs Performance (Tomshardware has recent articles which recommend graphics cards based on price.)
4) Physics? (some games have physics acceleration. If this is important, get an NVidia card.)
I'm playing a lot of fairly modern games based on the system at the bottom. I do wish I had a little better performance for some but I'm overall pretty happy. If you have a better CPU than mine I recommend a faster card than a 9800GT. It depends on your gaming habits too.
While not much faster than a 9800GT, the HD4770 is the most power efficient and quiet card you can buy for it's performance level due to its 40nm die size.
Not all cards of the same model (i.e. 9800GT) are equal. Don't overspend, but also don't get one of the cheaper cards which may sacrifice slightly on build quality. Read a few reviews and/or comments and shop around for prices online.
My system:
X2-4800+
HD3870 512MB
2GB DDR3200
WD 300GB Velociraptor; WD 1TB Green
Auzentech Forte X-Fi audio card + M-Audio AV40 2.0 speakers
*There's a guide for CPU performance comparison. You can use this as a ROUGH guide to the maximum graphics card you can buy. Assume the HD4770 is the maximum a X2-4800+ can support. Use the performance ratio of your CPU vs mine then compare to the FPS ratio of the card you want compared to and HD4770. For example, if your CPU ha 2x the performance ratio you can get a card with about 2x the same FPS in games.
The above method isn't perfect mainly because modern cards are usually compared with the same high-end CPU like an Intel i7 920, but it's a rough guide. If going SLI or Crossfire is important ensure you have a high-end CPU that supports two cards. There can be lots of issues with SLI/Crossfire (especially noise and power) so carefully read up on this if you go this route. You can get a really great game experience with a high-end graphics card so I personally don't recommend this route.
At $300 for the PS3 SLIM I'm debating buying one of these and not upgrading my current system and use both for gaming.