Index a file share with SharePoint 2010

Give SP search account read rights for the shared folder. To find which user it is:

Central Administration->Application Management->Manage Service Applications->Search Service Application
And look under System Status for:
example:
Default content access account CONTOSO\sp_service

Next add your share to the content sources:
Central Administration->Application Management->Manage Service Applications->Search Service Application->Content Sources->New Content Source
And choose FileShares (fill other values)