Imac Network Help..slow and droping?

So I am making the switch tonight from my old PC to the new Imac. I have a cable modem connected to the mac which works flawlessly with my macbook pro.

Tonight I am transferring data via wireless to the imac and it seems whcn I have 2 c onnections going liek itunes store and software updates the connection dies.

So I decide to attach it via ethernet and now it works without dropping but my connection download speed went from 2700 to 600k from the speakeasy test.
Any suggestions?

Now an odd thing...

I have hooked both my pc and my imac up to the router and the pc is reporting 4671 dopwn and the mac only reports 2073 from the speedtest.net test..

is their a setting I need to change on my nic card?