You are REALLY pushing the Hard drive free space.  I don't know my ATI cards very well even though I own one, but I think yours is below the recommended specs.  Maybe a more qualified person can make it more clear on whether you can or not.

You will need to do some serious upgrading to this machine to run Dragon Age... Given you say you don't know anything about computers I would recommend getting a new computer if you have the funds available. Check newegg.com, tigerdirect.com or microcenter.com for pricing. Your local best buy may also price match, etc.

Here is my reasoning for this.
1) Your cpu is already at the minimum for running this game (not good). However, you could upgrade the cpu which is easy on AMD boards.
2) Your ram doesn't meet minimum requirements as you need atleast 1.5 GB of RAM.
3) Your graphics card is most likely integrated (not good). You would need to upgrade to a better graphics card.
4) As stated by Tater, you hard drive is severly used up. It would not be a good idea to fill your harddrive 100%. You could of course un-install some programs to make room.

It's simply hard to recommend upgrading a computer like this when newer faster computers are available for fairly decent prices. If you are intent on upgrading you will at a minimum need to free the harddrive space, purchase more ram and upgrade the graphics card. Assuming you meet the minimum requirements listed you should be able to play the game. Good luck.

Minimum Requirements

The cheapest way to get a new computer these days is if you have the cash to buy the parts and a decent computer shop in your town somewhere. I'm talking about a custom shop/small business, not Best Buy or Curium City. All you'll really need is a new motherboard, a processor chip, a new graphics card (most expensive part usually), and memory. A new Hard Drive isn't that expensive these days but you can always just use the one you have now (but you'll need to free up some space). If the DvD Drive on your current system is ok then have them put it in your new build. You can save a lot of money doing it this way and you can probably re-use a lot of the parts you have now.

There's also going the "package deal" route and getting a Dell or a Gateway or some other system like that. They do financing and monthly payments and if you know what parts you want and are willing to pay a little more you can go online or to Best Buy and custom build one. Usually you can even get them insured at the larger stores. If you do it this way though instead of buying the parts and having it put together for you at a smaller store you Will Be Overcharged. Smaller stores can often get their parts straight from a distributer of the manufacturer and get the same warranties only at wholesale prices. That way you don't get huge fee's tacked on by Del or Best Buy or any other middle men. The package deal companies though usually come with good customer support. Sometimes though their version of certain parts are less powerful then that same part you could buy off the shelf. Also you may have to send your whole computer back to a place across the country to get it fixed if something goes wrong.

We can tell from your post that you aren't too familiar with the hardware side of computers, but hey, that's ok. There's nothing wrong with that. We all had to start to learn somewhere. Honestly, it's not as daunting as it may seem at first and you don't need to be a rocket scientist to be able to piece together a decent system. Once you get this figured out you'll be able to save yourself a Lot of money. Buying the parts and putting them together yourself is even better then having a shop put it together for you because you save money on labor. Until you get to the point you Really know what you're doing though I don't recommend that for the average user. You can fry a hard drive just by touching it if you aren't properly grounded and static free. There are a lot of things that can go wrong with parts as well if they aren't properly installed. Not having a peripheral "seated" correctly on the motherboard can mess your day all up....trust me on that.

If you do your research though you could build a $3,500 Alienware system for about $2,000 and the only difference will be the "Alienware" sticker on the case. You just have to shop around and order a lot of parts from the manufacturer or a web-site. 

Thanks Raven X and ZombiesRus5; it's always good to see additional info.

As a side note, if you want to learn about computers, building your own from scratch is one of the greatest teachers.  There are plenty of good resources online for information on the do's/don'ts, and the sense of accomplishment when it's all together is fantastic.  I'm sure the posters above can attest to this.

For a graphics card get the ATI Radeon 5750 which can be had for $99 to $129 bucks.  5770 is around $150.  These are the low end of the latest ATI and even they blow away most Nvidia cards right now.  The pendulem is swinging back to ATI.  Plus with the 5000 series you have full DirectX 11 support with Windows 7 so you are ready to go with any new DirectX 10/11 games.

I have a 2 year old ATI 3870 and I'm running the game at 70 fps at 1440x900 on high with no AA.  I went down to 1280 x800 and now run it on very high with AA on and get a steady 50 fps.  Looks great.  All this on my 2 yr old Core 2 Duo 3.0 ghz with 2 gigs of RAM on XP.  A 5750 alone will blow away my frames so you don't need to spend a whole lot to get great frames unless you want 1600x1200 or higher.

Oh, I don't run my games at any higher resolution because I can't read the text with my old eyes.