hey i have an old compaq presario 5320us in my basement and i was just wondering, could i replace its 478pin 1.6ghz p4 with a 478pin c2d? ty

Your Presario would never support an Intel Core 2 Duo processor. It's a little like asking "Could I swap the engine in my Chevy Nova for one out of a Dodge Viper?". Even if you could fit the new unit in the same hole (and I'm not convinced that you can), nothing else would link up. Everything else needs to be made more powerful to cope with the bigger demands of the new unit and your old system was never designed to do that.

If you want a technical explanation rather than my little analogy, your motherboard only runs processors with a 133MHz FSB, whereas Core 2 Duo processors are running at 533MHz, 800MHz and 1066MHz FSB speeds.