Don't bother 5-boxing on a dual core with 2GB of memory. Get another 2GB at a minimum. Then you will really want to consider a quad-core. I 5-boxed with an overclocked E6600, 4GB ram, and 8800GTX for months.. but that system is pushing it hard to be playable. You'll be "able" to 5-box with 4GB on your system, but you may not like how you have to limit fps on the followers and still get bad performance at times on the main, especially in outlands/northrend.

A Core i7 920 with 4+GB of memory is a big upgrade from an E6600, but not as much from a Q6600..