First of all what kind of connection do you use for internet access and how fast is it?

If you are trying to download a big game over the internet on DSL it will take forever. Cable Broadband Modem is much faster.

Another place that will slow your computer's ability to process downloads fast is the RAM on the computer. Usually eMachines only came with 128MB of RAM. EMachines is now owned by Gateway. You need to know what Motherboard you have and what its memory standard is. For example, PC 3200 will not work or fit in a PC 100 computer. Usually when you find your computer's owners manual on line (gateway.com!) when you find where it says "RAM" it will say if it is PC 100, PC 400, PC 1000 etc. I would not be surprised if it only had PC100 memory which can be had for pretty cheap. Put a pair of 512MB RAM sticks in it and watch it go much faster. Corsair Valueselect is inexpensive and very good RAM. No need to OC and you can't do it with an Emachines anyway. Also one thing about RAM and windows XP: You cannot CANNOT mix and match RAM sticks like you could with Windows 98. If you have two RAM slots you must use two sticks of the same kind of RAM. If you have four they all must be the same type. If not it will prevent your computer from operating correctly and it will function slow if it does at all.

I do not know what Anti Virus software you are running but it sounds like you may also have a boot sector infection. Also depending on the infection you may have on your computer I would advise installing Avast Home Edition and let it run a boot sector scan but keep in mind you cannot use two different Anti Virus softwares on the same machine at the same time. Avast caught stuff Norton and PC CIllin missed and both are pay to use softwares! Avast doing its boot sector scan catches stuff before it has a chance to shield itself from removal and a lot of malware copies itself to your restore files and a lot of anti spyware software will miss it. There is a program called SpywareBlaster which is a handy supplemental shield against malware. Majorgeeks.com has a lot of nifty apps for helping deal with crap in your PC. C Cleaner is one program that will help speed up your PC a lot! I recommend you give that one a spin adn see what you get.

what BrettBrett has suggested, is the proper way to check on your system. Also it's not a bad idea to DEFRAG your hard drive as well.
If your hard drive is too fragmented, it will run slow and may even crash from time to time.
You can overclock if you want to, but I don't recomend it. Usually your board is already overclocked to a safe maximum speed. Going past that can burn out your processor, memory, even your motherboard and hard drives.
Formating is a quick way out, but is still no guarentee that your system will run any faster.
Rule of thumb, Memory is a key. If it's XP, you want at least 64megs just for the OS, and I would recommend that you figure out which program uses the most memory. Add the 64 to that and double it on your computer (if it can handle it).
Processor also needs to be relatively powerful as well.
WARNING! If you are using hyperthreading on your processor, I would strongly advise against overclocking. You can burn out your processor in a matter of months or weeks.

you need to fill up mr fusion