Should I overclock a dying PC?
Overclocking a laptop is a risky move, overclocking this particular laptop is more.
As you know, most laptop BIOS don't support overclocking and heat-dissipation will be a real problem as well. Moreover, a few more MHz don't mean substantially better performance.
I suggest for you to replace the HDD. A new HDD with higher RPM and a better cache would make a real performance difference, you could look at (for example) the WD Scorpio Black.
So responding to your answer:
No, you don't; and probably you can't
CPUworld says 95°C is absolute maximum temperature
If you replace the HDD, you would definitely see a performance boost, especially boot times and file access
From AMD Sempron 3300+ Processor Review :
The overclocking side was a bit more difficult than with a comparable Athlon 64 or Athlon 64 FX, as although the Sempron 3300+ supports Cool 'n Quiet technology, it had no facility to downshift the multipliers on our reference systems. That made any overclocking attempt one of purely increasing clock speed, which we managed to attain up to a 236 MHz speed, which resulted in a 2.36 GHz core at 1.5V to 1.525V.