For more information see the HRCP reports (the sections 'Weapon/method used' contain a complete breakdown of these statistics).
2009 Report: http://www.hrcp-web.org/PDF/2009%20-%20Killings.pdf
2008 Report: http://www.hrcp-web.org/PDF/2008%20-%20Killings.pdf
Under-reported?
It is unclear whether there is an actual rise in such attacks on women or whether there is a rise in the reporting of such attacks. Either way, there is evidence that cases of violence are under-reported.
On a related note, in June 2009 Awaz CDS conducted surveys in the 4 Districts of Southern Punjab (Multan, Muzaffar Garh, Jampur & DG Khan). 94% of respondents said they had been threatened by a gun, and 70% believed the gun was held illegally. There has been progress in Pakistan where the Domestic Violence (Prevention and Protection) Bill was passed by the National Assembly on 4 August 2009. However, armed domestic violence has not been acknowledged.