I'll be as honest as I can... no it'll probably not be worth buying a CSPPC for the machine, and that's only cause it'll probably going to cost you a hole lot more than what you're getting back from it.
Not many games take advantage of the PPC and MP3 playng/web browsing will be possible on much lower specced computer (even a 040/25 should be sufficient enough for most).
Now don't get me wrong though, do you find it for cheap go for it, but you'll probably be ok with at least a 040/40 or 060/50 board.
The good thing with your computer is you already got a flying graphic card so it'll do much for the system... a netcard too ofcause. Hopefully there'll be other drivers available for you if not already then in time so you can use cheap soundcards also.
Prices CSPPC040 (060 will go for 50Euro more)
<200Euro : GOGOGO
200-350Euro : Got the meney? GOGOGO
>350Euro : Isn't there better options?
Prices 060
<100Euro : GOGOGO
100-200Euro : Got the meney? GOGOGO
>200Euro : Isn't there better options?
Prices 040/40
<60Euro : GOGOGO
60-150Euro : Got the meney? GOGOGO
>150Euro : not worth it, overclock your 040/25-33
Prices 040/25
<20Euro : GOGOGO
20-60Euro : Got the meney? GOGOGO
>60Euro : Find a better deal
