It has been a while since I posted anything here. I'm not sure if anyone has discovered this yet. Like many 5800 users I am unhappy with lack of games for S60 5th. I recently discovered by accident that you can use a lot of flash based games on the 5800 by simply running the SWF file. It gets a bit tricky coz with v11 firmware you could play it on fullscreen but on V20 you need to open it up with the s60 browser. Sometimes you need to edit the HTML file to play in fullscreen.
Here is an example. Go to a site that allows you to download SWF files like http://www.crazymonkeygames.com/download.php as an example download a game like Mass Attack. You will get 2 files one which is massattack.swf and another one called code.txt. Edit the file code.txt and change the height to 360 and width to 640 and safe it a massattack.html.
Create a new folder on your phone (memory card) called Mass Attack and copy both files to it. Now open the massattack.html with file manager which should launch the browser and play the game.
Stick to games that use the mouse, keyboard based games usually don't work.
Like I said i'm not sure if anyone has done this before. Anyway, I hope someone finds this useful.
Cheers!
Zap