Edit: That RAM looks kind of cheap. I have about 400-500 dollars to spend..im not saying give me the most expensive kind but im not on a tight budget here..and I hope to keep this computer for years and years..Ive already had it for almost 3..it still runs quick as hell but I want it faster. This is my main desktop computer but I also have a macbook pro.
The ram is $30 including delivery. 4GB will be $120. It is DDR2 RAM, which isnt the newest and quickest ram (DDR3) so you wont get blistering performance to match the newest system. (And even if you could utilise DDR3, in the 'years to come' it wont be future proof as things will be brought in and refined)
It will however, improve your system a fair bit. I wouldnt spend any more on anything else really.. Save your money invest in a new system in a few years, and pick up a DDR3 compatible mobo then or something.
Just because its cheap it doesnt mean it wont do the job
Just because you have a budget doesnt mean you have to spend it all.
Upgrade first, and see the difference, then decide if you need more.