On this website www.thetechguys.co.uk, it says this;
CPU Support
Socket 478:
Intel® Pentium® 4 processor
400 MHz system bus with an integrated 256K L2 cache
Intel® Celeron® processor 1.7Ghz >

CPU Support
Socket 478 for Intel® Pentium® 4 / Celeron® D (Prescott, Northwood, Willamate) processors
FSB 800/533 MHz
Supports Hyper-Threading Technology
Supports Untied Overclocking Technology

It even says in my motherboard manual something about Intel P4 in the mPGA 478 pin package. I have a Intel Celeron 2.40GHz at the moment and am thinking about upgrading parts of my PC so I can play modern day games. Does the info above mean that my Motherboard can/should take/handle a Intel P4?

Yes it should be OK but a 2400mhz Skt478 Celeron is not a modern gaming system, you are talking 3 year old technology. I presume you have an eMachine or an EI Systems Tower as you mention the "notechyguys aka PCWORLD UK"

There is a Gaming Forum at CN which has lots of posts about playing recent games and requirements....

Thanks for responding yer I have an eMachines 410 which is about 3-4 yrs old. Can't afford to buy a completely new PC so trying to get new (well ether new or used) parts for as little as I can. I'm looking at CPU's on ebay at the moment and there are a few Intel P4 2GHz+ going for about £3+.

It doesn't say anywhere on that website I mentioned or in my manual as to what GHz the Intel P4 should be should I go for a 2.4 or can I go for a higher one?

The CPU is the least of your worries. For "modern gaming" you'll need a decent video card, plus most gamers would recommend 2GB RAM.

eMachines is notorious for using crappy Bestec power supplies, so chances are, that will need to be upgraded to be able to handle the load of a gaming video card. I'm guessing that your board has an AGP slot? AGP cards are a dying breed so the best card available would be the Radeon HD3850...it doesn't get any better & probably never will. I just did a quick search & found one at Amazon.com for £138.81:

http://www.amazon.co.uk/Club-3D-385...

Tally it all up...CPU, RAM, video card, power supply. Is it worth investing that kinda money in a 3-4 yr old eMachines?

"And that's the fishing line, because Sharkboy said so!"

The eMachines uses a Trigem Imperial-G Motherboard:

http://www.e4allupgraders.info/dir1...

http://www.e4allupgraders.info/dir1...

http://www.e4allupgraders.info/

It may be feasible to go up to P4 2800mhz, but considering the base unit only has a value of around £50.00 it would be better to sell and buy a used newer base unit.