Your board + psu probally would not accept a modern card , meh u could scrape buy with a quick drop in upgrade.
PC Parts are sold from resellers like that dude said Newegg. In Uk you use Ebuyer, Dabs or Scan. What you do not do is walk into a PC shop and pay them. That costs you a arm and a leg. Dell is about its own product range etc with other manufactor's . Its cheapest best and yeh
Do not worry about ur return rights 3 magic letters "RMA" - Us PC users have a good life. If a product doesn't meet expectations RMA it. Simple full money back. Goto a good place with good reviews and yeh, you will want to not aim too high with the GPU. Everythings just gona bottleneck and you could find a bargin, also doubt u got a proper case. Tbh starting to try and figure out what PC u got i can see this
You probally got a Micro series case. Not modern or decent GFX card will fit in this.
Your mobo + ram is just appauling for gaming
You wanna upgrade your GPU to a beast or something?
Spend some time researching on the net and go for a full rig mate. Cheap and effective designed for drop upgrades in the future. Big case lots o fans, Good PSU , high end ATI 6k series or Nvidia 600 series. Gotta go high end, aka the 5990 not the 5330 or the 6990 not 6330 thats what i mean by high end. Later edition of that products generation .always research what ur buying, what potential faults could come with the said part. Then finally im gona say this ^ USE Newegg. If it has the PC building service in your area it really would save you alot of sweat. Your first PC build u sweat man, its scary or u wing it like i did blow ur mobo /shrug (i was youngling)
Newegg is trustworthy. More trustworthy then the companys who sell you a PC full off other products that affect its performance. OEM PC's are nasty world of hurt. Join us in the Gaming PC world bro.
I promise you this, you try and drop a new GPU in your PC you will start on a very expensive road. Your gona upgrade you can save proper value for money by buying "brack frida bundles" or "bundles" =D
AMD make very good value for money parts. Nvidia + Intel ur paying for the name .. AMD your paying what they think u shld for that sorta power. There method is fairer on your wallet. Also due to a past of lessor market interest, they have cheaper prices (but are better then the other 2 easily) - Everyone could argue me all day on this. Tis whats so good about the decisions u must make now
Just my advice
Dont let some shirt wearing boy rip you off on a overpriced GPU because you want to physically buy it. The price difference stupid, the service differnce stupid. Put it this way so few off us do what your thinking about doing you probally would never be able to return it to said shop and they would laugh you out.
advice nothin more enjoy
2 usefull sites
http://www.cpubenchmark.net/
http://www.videocardbenchmark.net/
I have a very sneaky feeling your board is a AGP slotset for that card, Pretty much any upgrade GFX card will not work. If you have any kids right now, use there future and IT stability to open that dam wallet of yours sir~!
edit : https://www.youtube.com/watch?v=zcR8Fl8cwZk