Multi threading with forms

This is so that when one of the forms shows a dialog, the other forms can still be used by the user and in effect the forms are independent of each other.

The problem is, if I use .Show to show the sub forms, the forms closes immediately after opening and the thread ends.

I've got around that problem by using .ShowDialog but this leads to other funny problems such as the form not closing when third party controls are added.

Is there a better solution, either to keep the sub form up using .Show or is .ShowDialog the only way to keep the form up and running?

Or is there something i missed with the .ShowDialog that might have created the problems with the third party controls?