According to emachine's website, your pc has a pci-e 2.0 16x slot available, which means you can install a decent video card.

It also says you have a 250w power supply, which means you'll probably have to get a bigger one to support a decent video card.

You also need to make sure there's room in the case for any add on card you want to install. Most video cards these days will also require 1 more more dedicated power cables from the power supply, and you'll need a power supply that has those outputs, or else you'll need adaptors to get that power from spare molex connectors.

It may be possible to get a basic video card for less than 100$ that you could run using your existing power supply. Check newegg. They have a power supply calculator page there that you can use to see if your power supply can supply enough wattage for any card you're interested in.

http://educations.newegg.com/tool/psucalc/index.ht...

Ok actually I've run your specs through that calculator just now and it looks like your current power supply is just barely sufficient to run your setup as it is, you're probably going to need a bigger power supply no matter what video card you get. It would be tough to do this for less than 100$ and get a decent upgrade out of it. Under 200$ would pretty doable.

A video card will be mandatory, and if you want a decent video card, a new power supply will have to go with it. $150-200 can get you both and turn that into a pretty decent gaming rig.

Graphics card. The processor is acceptable, not at all powerful, but what you really need is a discrete GPU.