Here's what Microsoft claims a P4 2.4 can't handle - A high-defination Video.
It asks for a minimum 2.53Ghz CPU to start with. Copy from their webpage:

High Definition Quality with Windows Media Video 9 Professional

Download the following clips to experience high definition Windows Media Video.
To deliver ultra-high quality, these clips were encoded 24 fps, and at the
resolution noted of either 1280 x 720 (720p) or 1920 x 1280 (1080p).
Although other system configurations may be able to playback this content, for
an optimal experience we recommend systems of at least a 2.53 GHz Intel or AMD
Athlon XP 2200+ or higher processor for 720p and 3.0GHz or greater processor for
1080p. For either scenario, an AGP4x based NVIDIA or ATI video adapter card with
at least 32 MB of RAM and the most recent OEM driver updates is recommended.

The higher the data rate (in Mbps), the higher the resource requirement. For
optimal playback of 1080p content, an AGP8x 128MB video card such as the ATI
Radeon 9800 Pro series is required. Learn more about Windows Media High
Definition.


The link is at

http://windowsmedia.com/9series/Demo...p=VideoQuality


In article , online says...

Someone I know bought a buget PC some time back. What
surpriced him was that his computer couldn't run a piece of
graphic-intensive game that he bought for his kids. I think
the game was called 'Unreal' or something.

I don't want something like that to happen with my upcoming
purchase. Maybe I don't use some software yet. But I want
to know what software P4 2.4Ghz CPU with 256MB DDR RAM can't
handle excluding those server software and business oriented
software.