What for? Your machine runs too slow to edit a 3D model? Or is your game running too slow?
There's actually a stark difference between the two.
If it's a casual game, or you're editing a low-poly model for a fun game project and not exactly a precise architectural complex, then you won't need a "quad core" at all. Trust me... been there, done that. The performance improvement even for multi-tasking is not exactly that high, and that's saying... I was using a 4GHz quad-core.
If you're playing a very demanding game, or you play games and render things at the same time, or you encode stuffs, then yeah, the quad will help.
Hell, nowadays, I find it hard to find the difference between multi-tasking with a decent single-core processor and any processor with more than two cores. Provided your OS and softwares are tweaked alright, that is. Having too many keyloggers or Trojans or adwares monitoring your system can potentially slow things down a lot.
And you definitely don't need an Antivirus or anti-adware, spyware, or popup blocker software unless you want to lose like 50% of your performance for nothing at all. Just don't open weird stuffs or visit weird websites and you'll be fine. Psh... get pr0n from trusted sources... and better yet, pay for them.