I upgraded from a GF2 Ti200 to an FX5200 and my performance just went through the roof. I'm not saying it's a fast card but it's sure faster than a GF2 lol.
Is the 5200 crap? Not really, just don't expect too much out of it.
As for overclocking, you can get a good 10% boost overall out of overclocking.
I overclocked my 5200 using CoolBits
http://www.overclockers.com.au/files/CoolBits.reg
A manual for it is on this page
http://www.overclockers.com.au/techstuff/a_coolbits/
Just for referance
Card: MSI made GeForce FX5200 (non ultra)
Initial memory speed: 400mhz
Overclocked memory speed: 451mhz
Initial 2D core speed: 250mhz
Overclocked 2D core speed: 291mhz
Initial 3D core speed: 250mhz
Overclocked 3D core speed: 291mhz
Any higher than about 291mhz and games start to almost freeze up. It took me about 3 minutes to exit JK2 when I overclocked the 3D core too much! If you put the memory higher than 450 or so, the screen just goes black and you have to restart.