Comparing the 64-bit to a Pentium 4 is a bit like comparing a jumbo jet and a concorde. The 64-bit part is sheer processing power, not something that an average home user wants. It is like buying Schumacher’s Ferrari and then driving it down the narrow bylanes of Old Delhi - a Maruti would be more suitable there.
Costwise too, the 64-bit fellow costs an arm, a leg and then some more.
Ask yourself . do you REALLY need that much of processing power if all you want to do is play games, video/voice chat and surf the net(since most of these activities depend NOT on the processor, but the VSNL network speed).
A 64-bit machine would make sense if you plan on dedicating it to some memory-intensive AutoCAD project, animation, video capture(and I mean professionally digitise video) or even SETI . then worth both the cost and the effort since more data can be processed in a lesser time span. Otherwise, a P4 is a safe bet . or as I call it: SST (Sasta, Sunder aur Tikau).