I need to inform a tech of which way to go. the p4 is $250 australian and
the celeron is only $130. so will I notice much difference for games etc? is
the extra price worth it?
In general, yes it's very helpful for gaming.
However, if you don't have a fairly strong video card too, the
savings might be better spent on a video card upgrade.
Similarly, the memory should be minimum of 512MB but preferribly
at least 768MB or more... in other words, pick whichever best
matches the other system specs, there's not any single component
that can be splurged on that will offset other major bottlenecks
(enough) in gaming.
If you happened to be an overclocker, you might find a lot of
headroom in either CPU, making video card even more significant a
factor.
Frankly (assuming you're building a new system) if you want the
best bang for the buck in gaming you ought to consider an Athlon
Barton instead. An $83 Athlon XP2800 (current pricewatch.com
pricing) is faster than a 2.4 Celeron, and overclocks pretty well
too... even more $ left over for great video card or monitor
upgrade, etc.