Need help to identify this part on a Vostro 1500

Can someone tell me what this chip is? Is it the CPU? I want to buy a thermal pad for it as it's cracked. Btw I replaced the thermal paste under the large heatsink on the left.

 

You replaced the thermal paste on cpu,
and the chip you asked is the northbridge

 

Thanks, is it advisable to remove the thermal pad from the chipset and replace it with thermal paste only or will there be too big of a gap for the paste to be effective?

 

If the old thermal pad is still able to cover the northbridge die,
I would leave it there..

If not, it's better to replace it with thermal pad instead of thermal paste ..
I think it will have a gap.

 

OK thanks, do you have any links where I could buy a thermal pad for the Northbrige chip? I tried Google and nothing I saw looked like was under the chip.

 

It's not a specific pad for northbridge, you can just search for thermal pad in local computer stores.
Or in ebay like here: http://cgi.ebay.com/Thermal-Pad-100x200-2mm-thickness-Dell-Xbox360-GPU-CPU-/320493627891

another alternative is to put copper shim + thermal paste..
ask a member: Ktron, he has lots of shims.. or at ebay .Goodluck!