Hi Mattias,
Welcome to the Ranch, we are happy to have you here:)
Unfortunately, you haven't specified what kind of problems you are facing in "running" java.
Check out
this link. It has all kinds of useful information on common problems.
For text pad to work correctly (and automatically), the JDK needs to be installed properly. So your two problems are probably interrelated.
Regarding the GUI stuff, I would suggest the following procedure
1) Identify all the required functionality.
2) Identify all the objects you are going to require.
3) Identify how your UI should look and perform, what the process flow is, what the user experience should be.
4) Figure out how you are going to use the objects in #2 above and integrate them with the UI components. Remember, having the MVC is a big plus.
5) Then you get to actual coding!!!
The ranch is a very friendly forum with lots of people happy to lend you a helping hand. All they expect is you put in the initial effort. Fortunately, you think on the same lines too, as you are not looking for ready made stuff but you want to build it yourself.
In case you haven't done so already,
this is sure to help you get the most out of the ranch.
Best of luck. Go for it :)