OK, it seems overclocking is the first step; so, HOW do I overclock? To be honest, I've heard of it before, but I have NO IDEA what it is...
based on your motherboard there's a certain process in bios although most are the same. I would google your cpu and get the settings other used successfully (FSB, multiplier, core voltage is what you're looking for - there are more settings but i don't think you want to push the envelope too far). Then look for your memory and get the O/C specs for that, I run my DDR2800 at about 900MHz with 2.1v (but that can be different for your DIMMs so don't take that as the setting you should use) - i also have the FSB and memory at 1:1 which I understand gives the best performance, FSB is 1800 from 1333 stock.
You will also need a really good heatsink (or you'll fry the CPU) and possibly lap the CPU as well (I did that and it gave me about 5 deg drop, but that depends on what you start with, if it's flat to begin with you might not need or get as good of an improvement). The other thing is the thermal paste that goes in between the heatsink and the CPU, there are 2 types you will want to use, 1 is ceramic (preferred) and the other one is called silver something (can't remember, it's been almost 2 years since i did my setup) - this silver one is a bit dangerous as it's conductive so you need to be very careful with it.
You might also want a memory cooler, they are fairly cheap, its a dual fan module that snaps on top of the DIMMs - keeps them cooler when you o/c and increase the voltage.
PCI express speed can also be improved (i think i am at 112MHz from 100 standard but don't quote me on this as it's been a while since i looked in the bios) - also, is yours 16x, if it isn't then you'll get a bottleneck right there regardless how much you overclock.
the last one is your mobo chipset - before i watercooled my rig (in which i have a waterblock for the chipset) I had an upgraded heatsink with a fan to keep it cool
but this it all depends on how much you overclock, so imo if you can't get a decent increase in speed without too much investment you're probably better off getting a corei5 mobo, cpu and memory and a decent videocard (like Jeffy said, you can get a 9800 quite cheap these days) - it will outperform your q6600 any day.