No, you don't need a Crossfire for the 4850x2, at least I don't think so.
I would go for the GTX260, I've heard it outperforms the 4870 1GB, and comes close to the 4850X2, but uses much less power. Right now there is a Evga GTX260 Core216 on the Egg for $180, $160 AMIR with a free copy of COD5.
http://www.newegg.com/Product/Produc...82E16814130464
Although, you may want to update your sig-rig. If you're currently using a P4 I would upgrade that before I look at graphics cards.
I would go for the GTX260, I've heard it outperforms the 4870 1GB, and comes close to the 4850X2, but uses much less power. Right now there is a Evga GTX260 Core216 on the Egg for $180, $160 AMIR with a free copy of COD5.
http://www.newegg.com/Product/Produc...82E16814130464
Although, you may want to update your sig-rig. If you're currently using a P4 I would upgrade that before I look at graphics cards.