Upgrade or not...?

Hi !
I own a Shuttle and am unclear on how much I would really benefit from
upgrading certain components like CPU and graphics card and maybe one or
two other things. My current spec is this:

Motherboard: FB61
CPU: Intel 2.4 Ghz
Graphics Card: NVIDIA GeForce FX 5200
RAM: 1GB (2x512) (Windows picks up the full 1GB. The Siw tool only sees
512. Unsure about what to make of this.)

I am not a gamer but I like high performance and good graphics
nevertheless.
I sometimes watch TV on screen, and I use the internet a lot.

I would be very grateful for advice if it is worth the time and money to
upgrade thsi system or not.
Which components would be worth upgrading, and why? Or would the
difference in performance be too small to notice?
WOudl be very grateful for advice!

Regards
Johanna