The process to follow is:

1. Convert the *.pvk into a *.pfx file using the pvk2pfx tool.
This should be in your Program Files\\Microsoft Visual Studio 8\\Common7\\Tools\\Bin directory.

2. In Visual Studio 2005, go to Project->Properties->Signing tab.
Check Sign the assembly or both depending.
Click on the 'Choose the Strong Name Key' combo and select 'Browse'.
In the 'File Dialog' choose the *.pfx file you've created in step 1.

Click for more information on VSS and code signing from Microsoft