Greets.
The OC features of your card greatly depends on the cooling solution implemented by the laptop vendor.
As a general thumb rule, mobility cards are bad overclockers, not for the card themselves but for the poor cooling systems used in laptops.
Latest gaming powerhouses like Inspiron XPS or Alienware Area 51 have fairy good cooling solutions, while older models generally are Heat Power Plants even at stock clock speeds when pushed to limits, (Doom 3 for example

)
I have a Dell Inspiron 9100 (same chassis than Dell Inspiron XPS gen 1), and was able to slightly overclock my old MR9700 without significative increase in heat, and running 100% stable for extended gameplay sessions, (now I have a MR9800, and this card is indeed an even better overclocker, and truly awesome when paired with the Northwood core P4, cooler than the standard Prescott one, as the CPU and the GPU are phisically placed very near inside the chassis, thus 'sharing' the heat generated to some extent).
Anyway, before attempting to OC your card you should get some kind of Temperature Monitoring system, (Inspiron users know about the good old I8kfangui). And always watch your temps with each OC attempt.
Also, ATITool is a great software for OC your card, as it can watch for artifacts caused by the overspeed, and have some limited Temp Monitoring system (temp monitor works only on certain computers).
Nevertheless, always remember that OCing your card is neither recommended nor supported from laptop vendors, so do it at your own risk.
Good luck. Regards
L