First of all - I'm sorry for not commenting on this earlier.
I think there are several different issues here, so let me start by throwing out some general ideas; they may not all be relevant to your specific situation.
1. Check the logs, both c:/subsonic/subsonic.log and c:/program files/subsonic/log/subsonic-service.log
2. If you have a very large music collection, try increasing the memory limit (for instance from 100MB to 200MB).
3. Try turning off the search indexing (Settings > Search), and delete the search index file (c:/subsonic/subsonic*.index)
4. Disable automatic port forwarding (Settings > Network), and setup manual port forwarding on your router instead.
5. Use a different router if you have one available.
6. Upgrade to the latest java version.
7. Run jconsole (or even better jvisualvm) to debug the Java VM. This requires some familiarity with Java, but is an invaluable tool to detect memory leaks.
Personally I have three Subsonic servers running on Windows 7, Windows XP and Linux, and they run for months without any issues. Of course, that doesn't mean that there are no stability bugs in Subsonic - but it means that it makes it difficult for me to identify them.
If any of the suggestions above works for you, it would be most helpful if you report back (please include the details of your installation).
Thanks and sorry again for the late response!
Sindre