That's a tricky thing. Because really, having MORE RAM, doesn't speed up startup or program "loading". Because the bottleneck is not the ammount of RAM you have, but the speed at which programs can be loaded INTO RAM. Your hard drive will only pump data into RAM as fast as it can, ammount of RAM won't change that. To speed up startup and program loading, you would need a faster hard drive with better access times and transfer rates.
What more RAM does is allows Windows to cram more of your open programs into memory, thus allowing them to run at RAM speeds. Versus swap file speeds, which is millions of times slower than RAM.
A P4 2.4 isn't terrible, even for gaming. The biggest parts, in my own oppinion, for gaming, are in this order of importance:
1. Video card. It drives everything.
2. RAM. Allows your whole game to open in RAM.
3. CPU. Allows quicker number crunching.
4. Hard drive. Faster access speeds helps when loading new maps, loading games etc...
There's no point in having a gig of RAM and a 3000 P4 if you have a Radeon 9200. Games will still run like crap and look like crap. No point having a 3000+ and the fasted hard drive if you have 256 of RAM. You get the idea.
Hope that helps.
The particular benchmarks we're talking about can be found at
http://www.futuremark.com/
I believe they have demos but some tests and functionality may be disabled.
cheers