First of all, you will need to read through the Guide on the left to find out all the things you will need to be able to upload Games.  I suggest uploading a few ringtones and wallpapers before attempting to upload a Game.
 

Okay, to begin with, you will need a .jad and a .jar file.  Go to one of these sites to get them.

(if you have heard of any other worthwhile sites that have .jad and .jar sites pm me on HowardForums.com - john00)

Once you have downloaded the .jad and .jar for the game you want, open up BitPim and go to the filesystem tab and click the +.

Go down the ams section, and click the + symbol.

From here you will right click on ams and click new subdirectory.  Starting at 00 you will go up, so in my case the new subdirectory that I would make would be 08.

You will put nothing in this subdirectory, as it is used for saving games, etc.

Next, right click on ams again and click New File.  Go find the .jad you downloaded, and rename it to 08.jad (the name corresponds to the folder you just created).  Next, right click on ams again, click new file again, and find the .jar you downloaded and rename it to 08.jar, then select it.   Now, right click on contentInfo and save it to your desktop.

NOTE:  If you have not yet downloaded anything to your phone, you will not see any of this.

Click here to download a sample contentInfo file.

Open it in Notepad.  In my case it says:

Seems like a big jumble of words right now, but, if you press enter before each !C it will make it much easier to comprehend:

It now makes a bit more sense, and you can and should erase everything starting at !E down.

Now, copy the first line !C 0 NHL etc to just before the next !, and paste it at the bottom.  Change the number to correspond with before.  (8 for 08.jad) and change the name to what you would like to appear in the menu.  Where it says Games or Tools, you can change to make the file appear in whatever section you want.  You can also create new ones, say "Math Programs" or something like that.  DO NOT add a line in your .jad saying Folder: Games, as for some reason it has not worked with mine, and not allowed the game to start.

Now, unplug the phone, restart, and test it out!  This guide may still be buggy, as there have probably been minor things I have forgotten.  Any issues?  PM me!