Note:
This question refers to a very old version of jQuery.validate() (version 1.5). This plugin now provides a built-in solution for doing this: the .r
While there are other ways to do this ASP.net does allow you to use multiple form tags so long as they are not all rendered - so if you use a multi view to only display the relevant content you can use multiple forms.
It tends to clean up validation and submit handling quite a bit.
Alternatively jquery does allow :visible to be added to your selector, so you could potentially only run the selector on visible elements and sidestep the issue that way depending on how they are hidden.
How :visible is calculated was changed in jQuery 1.3.2. Element assumed as visible if it and its parents consumes space in document. CSS visibility isn't taken into account. The release notes outline the changes in more detail.
Here is a better / simpler solution from another post on stack overflow-
Apparently the validation plug-in allows you to specify :visible in your rules. Here is the post-
Advanced JQuery Validation: Avoiding Validations on Certain Conditions