ISA Server 2006 Block File and Form Upload

Right Click to your Access Rule and Choose "Configure HTTP". Choose signature tab from the new window.

Click Add Button. Enter the New Signatuer name (it can be whatever you want) . Choose "Request Headers" in Signature Search Criteria.

Type "Content-Type:" (except quotas) to HTTP header line.
Type "multipart/form-data" (except quotas) to signature .
Click OK and Apply.