Best two spyware tools, recommended by nearly all pc mags and pros.
1. Lavasoft's Ad-Aware SE (FREE)
2. Spybot's Search and Destroy (FREE)
Definately need to check your pc's specs vs what is recommended on the games mentioned. Instead of Ebay I would check www.newegg.com. Great prices, fast shipping, very reliable.
Upgrading cost is very much dependent on what you currently have.
For memory: ($50 to $150)
What type of memory are you running, what type of cpu and motherboard do you have? Many times the max amount of memory isn't always the best because it also will decrease the speed a which the cpu can talk to the memory.
For Graphics:($200 to $600)
What type of video card slots do you have? What type/how many watts of power source do have? Do your games prefer Nvidia or ATI?
I forgot to mention that installation is very simple. Just need to follow some basic rules. Absolutely NO magnetic charge on your person. You should get a wrist strap to ground yourself. The memory just fits in a slot, if it is dual memory then you will have two cards that go in corresponding blue and black slots. Should be similar to what is already there. The GPU will have a similar slot but the added peice of a wire to the power source. Either way make sure you are grounded, clean, and dry. Don't touch the metal parts, only keep hands on edges of boards. Kinda like holding a cd/dvd from center hole and edge only.