Is it generally easy to customize a store-bought PC? I plan on buying a desktop from a friend, but the video card seems to be dead and I was considering replacing whatever card that's in it with a Sapphire Radeon HD 7770 card.

I don't know anything about the specs of the PC at the moment, since it can't really start up and he won't be bothered to open it up, but since it's store-bought I figured I can just google the model or whatever and figure out what is most likely in it before I make a final decision.

Of course, if I knew what was in it I'd be able to better describe it, but the only thing I can remember about it is that it was running on a DVI monitor with Vista, which I plan to replace with Windows 7, and that it was a Compaq.

So, is it generally not too difficult to replace the video card in a store-bought machine? Once I get him to drag it out later so I can look up the specs of it, I'll update.

I'm not sure about the specifics, but generally, most desktop computers that are not all-in-ones or nettops should be at least somewhat serviceable. If the case doesn't look big enough, a full-sized card may not fit.

It might be easier if I asked you what was the original video card inside the computer - if the original's a full size card, as long as the wattage doesn't go over the limit, you're good to go for the most part. (Do remember to check the power supply unit's wattage, too.)

While most of what Twiggy said is correct, I do have a comment on the wattage. Most OEM machines are built to safely (keeping the wattage below the rated maximum) accept about 50-100 watts worth of upgrades. You actually can go above the rating, but you run the risk of burning it out if they didn't do much testing, and you may lose the warranty. Odds are, unless you try to pack a bunch of hard drives and high-power cards in it, you don't need to worry at all about that.

It all depends on what kind of graphics slot is in there and how small the power supply is. I've done some upgrades on a store-bought PC in the past [first PC was a store-bought HP] but only upgraded the hard drives and optical drives.

What Twiggy says is true. Be very careful with that power supply. Most store-bought machines have power supplies that barely meet the power requirements of the machine. You may have to upgrade the power supply as well as the graphics card, which can be really hard to do. The PSU on my store-bought was only 250w. Good luck.

Probably not best to go by googling exclusively to decide if you can or cannot fit a part in. Open it up and check out the guts before you sink a hundred(or more) bucks into a new card. Also take some pics of inside the case to include with the specs, especially the motherboard, that'll be the most important part to know about considering that's where you'll be sticking the video card into. That and as others said, you need to figure out the wattage of the PSU, a normal card can take quite a bit of power and most of the pre-built sellers skimp on putting beefy power supplies in their machines to earn more.

Also, check this program out too: http://www.overclock.net/t/1045231/p...psu-calculator

I typically use this PSU calculator with a plethora of options, but that one looks more up-to-date.