Well I just asked basically this same question
and if I understand correctly, to get full speed
for a lot of games, you'd want about a 3.0
GHz C2D (e8400) and even that may need an
overclock for some games. Also, make sure it's a
"Core 2 Duo" and not a "Pentium Dual Core".
A graphics card is also needed.
The 8800 GT is a decent one for a reasonable price.
You also need to make sure the motherboard
has the right slot for your planned graphics card.
A decent graphics card also requires an upgraded
power supply that most machines don't come with.
For these reasons, it's often easier/cheaper to build
your own pc from a barebones kit, and add parts
one by one.
If you don't care about full speed, and don't mind
speedhacks that cause a bug here or there, then
you may do fine with the 2.4. (Or maybe you can
overclock the 2.4 to fast enough. You'd have to ask
someone more experienced if it's possible/safe.)
It requires a good graphics card either way.
Also, first check if the specific games you like will run.
(Check the screenshot/video and compatibility threads.)
If you're determined to put together a PC for PCSX2,
it's actually not that hard. Here are the basics.
You would first need to pick out a good PCI Express graphics card.
The Nvidia 8800 GT, 9800 GT,or maybe even a 7800 GT are good examples.
Make sure to get a PCI Express version, not just PCI.
You can probably get away with a GeForce 6600. Don't go below 6 for the
2nd number in the graphics card. Example: don't get a 6500 or 8400.
They don't perform nearly as good.
Then you need to grab a power supply that feeds the card. For any of
the above, a 650w supply should be alright. Make sure you get one with
good reviews. The Xigmatek NRP-MC651 is one good example. (Imo at least.
It works great for me.)
You then need to find a motherboard with at least 1 PCI-Express slot, and
some SATA (Serial ATA) ports. It's easy to check for these in the specs.
Again, look for specifically PCI Express, not just PCI. Sometimes you can
find a "barebones kit" that has a motherboard like this, plus the processor
that you want, a case, hard drive, etc.
If you are missing any of these items, grab
-A SATA hard drive
-A SATA DVD drive
-A cooling fan (This may be easiest to get at a local PC shop, where you can point out your case size.)
-The PC Case (Full Tower form factor is probably what you want.)
-The processor, of course!
-A tube of thermal paste. (Easy to find at most local PC shops.)
-An anti-static wrist strap. (Local PC shop.)
To figure out how to put this all together, you can look up youtube videos for things like
Socket 775 cpu install, motherboard installation, etc.
It's really not that difficult. (That's how I put mine together.) The most challenging parts
were putting on the CPU fan, correctly applying thermal paste and screwing spacers in
before the motherboard. None of them were that challenging though, especially with
youtube as a video guide.
You can actually find all these parts at these sites
for much cheaper than buying a pre-made equivalent.
(pretty good for barebones kits.)