[Solved] Will my computer support this?

Should be fine AFTER a PSU upgrade. No link to the PSU acution, so can't tell you if its enough. Also, pay attention to the size of the PSU your taking out. Being a HP, might not be a standard size to drop the new one in the case.

What resolution monitor do you play on?

That PSU will work for all the components if it will fit in the case. If that's your ONLY option for a PSU, then so be it, but that is far from a good PSU. The first indicator is the red switch on the back to choose the input voltage. Its a corner manufacturers cut and is usually a sign of the quality of the unit, or there lack of. Where the juice counts is in the amps on the +12v rails. You have 31amps combined, with is closer to a corsair 400w psu rating than the 500w. That being said, it is enough for the 9800GT. So you can see, they inflate some numbers and cut corners. Hopefully, it does start a fire when you go to use it.

The 9800GT can get 35 fps at 1920x1080 with full AA/AF, so you'll be great for L4D at 1440x900.
http://www.tomshardware.com/charts [...] ,1457.html

I feel I've failed you by missing this detail. How much ram do you have in your system? If its just the 1gb that HPs site listed, that would be the first and foremost upgrade to do. Vista uses close to 1gb by itself, so not a lot left for apps or games.

I've never heard of vantec over here. But it does have the same passive voltage selection switch that made me cautious of the first PSU you had listed. While the sale price seems tempting, the PSU is probably the most important part not to cut corners on. I'd still recommend the Silverstone of all the ones you've linked. My general rule is min of 3 year warranty and Active PFC to qualify as an acceptable part. What all websites are available to you to buy from? That might help finding an acceptable PSU at a good price.

Very few benchmarks you see out there are for a complete system. Most of the time, you want to see how an individual component will perform for the software its being tested for. So when you see a review and benchmarks for the 9800GT, they will put it into a powerhouse of a CPU system so that the program runs out of GPU power before it runs out of CPU power. Otherwise, the benchmark never really reports the true potential of the GPU. The 9800GT will be a good match for the E6600. If there is any bottlenecking, it will be minimal. These are well balanced parts.

The only way a PSU can bottleneck a system is if its not powerful enough for the CPU or GPU and they cause errors. Then you have to turn them down to keep it stable. Won't be an issue for you.

btw if anyone bothers to check you can run an E6600, 4gb, GTX260, 1 hdd and 1 cdrom with a good 300w PSU - did it with an AcBell without any hassles.

For a GTX 260 it seems like you need a Dual Slot, I only have 1 PCI-E slot

Well, if it can run L4D at full settings, I'm happy

So, I'll get the Silverstone fan, and the XFX 9800GT, thanks for the help.

Dual slot just means that's how much room the cooler takes up. The second slot plugs into nothing besides the case, and takes up the room and possibly limits you from running a card.

While it is low, its not a system breaker. I'd upgrade the other parts first and then see how it performs for you. You can always replace what you have later.