(First off, apologies to all pure Java folks, and non Windows platforms :-)

The following page shows using a combination of scripted (vbs) CAPICOM
and a utility Java applet (for MS JVM) to access the local file system.
It demonstrates CMS/PKCS#7 signing web-page form fields, entire web-page html content,
or any local file:
  http://pages.istar.ca/~neutron/clientsign

It requires IE5+, MS JVM, and CAPICOM COM component install (free MS tiny install).
It is possible, of course, to use Java 2 and some COM bridging components to access
CAPICOM  (CAPICOM has excellent hooks into Windows CryptoAPI certificate stores,
PKCS#7 messages etc..). Since MS JVM (has/had) excellent support for COM Variant
classes, this was the easiest approach to deploy web-based file and page signing capability
to a large number of Win users (Win5 - XP).

Just in case folks here didn't see the other Java/.NET article,  it discusses the more
basic PKCS#1 signature and compared Java and .NET capability:
  http://pages.istar.ca/~neutron/feature/RSAEncrypt.html

- Michel Gallant
  MVP Security
  http://pages.istar.ca/~neutron