Upgrading help :)

[Invent]

Hi,

As I've got a 3 month summer holiday, I decided that I'm going to take up a home project. So, in the past few days I've bought both a new Mac and an older model (G4).

During the holiday I am aiming to upgrade the older model to a reliable, working machine that can handle the latest version of OS X 10 as well as running memory intensive applications such as photoshop, dreamweaver, etc.

The specs on the G4 are:

Apple Power Mac G4 733 MHz Quicksilver
896 Mb RAM
40 GB Western Digital 7200 Hard Drive
nVidia GeForce2 MX 32Mb AGP graphics card
CD-RW (32x CD, 12x CD-R, 10x CD-RW)
Internal Modem

I am aiming to increase the ram and hard drive size at first and then probably install a DVD-RW drive and perhaps upgrade the graphics.

What I am wondering is though, am I able to upgrade the processor to give it a better speed? If so, could you please provide me links to any retailers if possible!

Oh and another question! Is OS X 10.5 much better than OS X 10.4? (as that was part of the point of trying to upgrade the processor).

Thanks,
Simon