Okay thanks for providing the right information. lol
As far as your gpu goes yes you can put that in even without upgrading your psu I'm sure. since its lower then 75 watts it should be okay unless you have a 200 watt psu but anything over 300 watts you should should be just fine.
You motherboard has one free pci slot at x16 which thats what you will need for your gpu and the gtx 520 is a really lowend card so power it needs isn't much i may be wrong but i believe its around 30watts which is really low for gpu's. It'll be really hard to find a stock psu that won't be able to run that card.
If you plan on gaming that card will help over intergrated gpu but it will not run the latest games. So if thats what you had in mind then you need to spend some money. It may run WoW and most other mmo's fine but when i comes to other games like (assasin creed, saints row the third, bf3) then you be out of luck.
Ok cool thanks and yeah I don't really plan on playing those high games such as BF3 but would I still be able to add the following I've listed and keep the processor i currently have in it? The processor is a AMD Athlon Processor LE-1640 2.7 GHz.
Would that processor be alright to keep the same if I add in the GT 520 and the 500 watt psu?
Well I think it will be alright its kinda tough to say for sure. Depending on what you have in mind. That cpu is a single core which most application and games uses 2 cores. Not saying it won't be able to run games or anything that uses more then one cores but you will just have to keep the settngs down low but your gpu is lowend so even if you had a quad core you will still have to keep the settings down low anyways.
As far as the power supply goes that will be way more then enough. I had a pc that uses over twice as much power as the one you have now and i was running it on a 480watt psu just to give you an idea. lol
What i would recommend you do is build a pc from scratch you can use some of your parts off the computer you have now like your hardrive and optical drive. Am2 is a dead socket now. You can probably get a decent lowend build for $400 it won't be amazing but it will have future upgradeablity and be better then the pc you have now.
Anyways back to your cpu it will do fine for web browsing not really for much else but for your motherboard the best cpu you can get is an athlon x2 6400 that cpu will speed up your pc by alot over your current cpu and allow you to run newer games. Also since AMD stop making those cpu's you will be spending more then you should on them. Once a cpu manufactures stop making a type of cpu's the prices rises cause you will only be able to buy them used. looking at ebay the prices are around $115 for the athlon x2 6400. Thats more then the phenom x4 955 new which the phenom's ii are also discontinue but retailers still have them in stock but once the stock runs out that prices will be higher.
this may be alot more information then you needed but if i didn't answer your question if you tell me what you plan on doing with it i can at lease say if it's capable with your system.
but everything is fine as far as the psu,cpu,gpu capatibility with eachother.