You cant really play the latest games on an HP/Dell/etc....

the cases are nonstandard and cramped so it generally means a long/dual width card cant fit, and netither can one with a large fan.

One thing you will definately need is an upgraded Power supply. Stock OEM PSUs are utter crap, they barely pump out enough current for your builds standard spec, let alone for any upgrading. They also dont have the connectors needed for running decent cards.

Dont skimp and get a cheapass PSU as a cheap "1000w" psu may only actually e.g 600w in practice.

The important thing to look for is what connectors it has for powering graphics cards. Most higher end GPUs will need 1 or more additional power leads, as well as the juice the draw from the slot itself. Its also very important to check out how many amps the 12v rail(s) are on any psu you intend to purchase, and compare that to the minimum levels reccomended by the graphics card manufacturer.

Again, upgrading your PSU may cause you hassle though, some OEM builds use entirely nonstandard power supplies too, although this is becoming rare. Physically inspect the unit and check the dimensions available. It aught to fit a standard ATX psu, but like I said, there are exceptions and it may be a very tight fit / reuqire some modifications.

You may also want to increase your budget as you will need to spend $60 to $120 on the PSU upgrade itself.

Once you are sure you can fit and power the cards, then i reccomend the following:

Low range cards: Geforce 8600 - Absolute minimum for current games. Will run current games on medium/low, older games on high/max. Around $70 to $100

Midrange cards: Geforce 8800, Geforce 9600

These are mid-high range cards and are $120 to $180 each. Will run current gen games on medium/high and older games on max.

If you want higher games performance look at the 9800 its $200 to $250 and is extremely powerful.

I dont know much about the ATI offerings but i hearr the HD4670 is meant to be okay. Roughly comprable to a 9600/8800.

nice idea jbennet

Totaly agree, id personaly swing nvidia`s way for the 9800 gt, dam good mid to high card, and coming down in price to

wanted to play latest games you should have bought a gaming computer not a home/office rig !with a 160 watt psu,and onboard graphics ,sell it and buy a gamer it will be cheaper that a new psu and video card if you could actually get one
and maybe the reason you haven't found any info on what to buy is because you don't come back to sites to see what people have to say ! 4 days now .
http://www.desktopreview.com/default.asp?newsID=416

160watt psu? Is that what the new core2s etc.... come with now?

Ive got a 3 year old dell with a pentium 4 and its stock is a (decent) 350w. Runs a pentium 4, 8600 etc... no problem. Maybe it just ships with a decent psu due to the fact that P4 is a power eater.

And yeah, i do agree. For most home/office users a readybuilt OEM machine is the best and cheapest option but If you want to have the ability to upgrade, or are a gamer, building your own is cheaper and easier in the long run and is the way to go.