finally got new HDD for my old computer

Now my question is how well will this old computer run games like hl2 and doom 3, if I got a new graphics card

its got a 1.8 ghz p4 processor, about 512 mb of ram and a voodoo graphics card... another question I can't identify this graphics card until I actually install the new hard drive how can I tell the cards specs?

I believe Everest will tell you what kind of video card you have.

Go to the Download section of Techspot, and type Everest in the search.

well I know that, but I can't get my computer on until I install the new Hard drive, and I was wondering if I could tell at startup or from just looking at the card.

sure it will work. Most games are more dependant on graphics cards than the CPU. Doom 3 will run better with a better graphics card, but what you have will work ok in moderate settings.

err... I get please insert system disk error now, anyone explain how to fix this.

You need a Windows startup floppy or go into the BIOS and set it to boot from your Windows CD. A Radeon 9800 Pro should work really well in your system. Since RAM is so cheap you should also go up to 1 gig unless you have RDRAM.