Currently, single core processors ARE better for gaming, but only because current games don't/can't take full advantage of having two cores on one chip. Here in the next 1.5 to 2 years though, new gaming engines will be released (upon which new games will be designed) that will be able to take full advantage of multiple cores/threads running together.
So, if your just interested with the here and now, or if you're looking to save money, go with the single core processor. You will still be able to run the new games that come out, you just won't get top performance.
BUT, if you want your system to still give you top performance 2 years from now, which is what it looks like if you're running two 7800GTX's, then spend the extra money and get a dual core processor.
P.S. This is just my little piece of advice. You make your own decision.
If you're truely looking into dual core processors you should at least check out AMD X2 dual cores. Currently, AMD seems to have better architecture for their dual core CPUs. Their two cores on the one chip are better integrated and can pass information back and forth at much higher rates of speed than Intel chips currently can.
Notice I've used the word "currently". Things CAN and often DO change when it comes to technology.
Don't just take mine, or anyone else's word for it when it come to technology and YOUR MONEY. Read reviews, look at benchmarks, ask what other people are using and how they like it, and finally MAKE YOUR OWN CHOICE. If Intel is the way you want to go, get it, and everyone else (myself included) be damned.
I know I sound preachy, but I just hate it when people make decsions completely based on info/advice from other people they don't know, and then come back later pissed off when they find out that info/advice didn't pan out.
There's my advice. That, along with a dollar will get you a 20 min phone call. Enjoy!