In Folder Options, View tab remove the tick from Use simple file sharing (Recommended). Right click on the folder you want to share and select 'Sharing & Security' click on the Permissions tab and set them accordingly.
You may also need to use the Group Policy Editor (Start, Run enter gpedit.msc and click OK) to set access for certain types of file. User Configuration, Adminstrative Templates, Windows Components, Attachment Manager. You can then set the default risk for file attachments and change the Inclusion List. I've modified mine to low risk and added e.g. .jpg.