I installed winpcap 4.0.2 from http://www.winpcap.org/install/default.htm and then installed the 32bit version of Wireshark (1.2.1). Maybe not the best option but it got me working and currently im not working large file.
I have installed, uninstalled and (clean) re-installed both versions, in the 64bit version the install
Fails because of the version of winPcap, the 32bit installs but is broken, giving winPcap errors.
Anyone able to provide steps to get Wireshark to work under Windows 7?