|"I was looking on the AMD website and I found some triple core processors at 45W, could I put those in my motherboard?"|
NO! You have to go with the Gateway recommendations:
"AMD® Athlon™ X2 processor (45 W max)
AMD Athlon processor
AMD Sempron™ processor"
"Would I have to solder anything or de-solder to install the CPU?"
Why is this so hard to understand?? Your motherboard only supports certain CPUs & that's all there is to it! There's nothing you can solder, no magic chip you can add, no miracle BIOS change that can be done. You have to stick to the limits of the hardware as stated at the Gateway site. If that's a problem, replace the motherboard with one that supports what you need.
"Actually, RAM and graphics card upgrades aren't what I need"
You can *probably* get by with just 2GB RAM, but if you're still using the onboard graphics, you should install a *real* video card. It doesn't have to be a $200 gaming card. There are plenty of video cards for well under $40 that will spank the sh!t out of your onboard graphics. And by using a discrete card, the memory that's used by the graphics can be returned to the system.
How about installing this $10 Geforce 8400GS? You could even enable the Hybrid SLi if you so desired.
The CPU isn't & shouldn't be the major concern, the graphics are what's important. Here's two better video cards for $20: