Alright, Petr Ga, and everyone else in the forum, I'll outline here how to break that 5fps limit and how to play the campaign with a decent system and the like. Some of these tricks require you to change the registry files for the game, but it doesn't mess with anything else.
First off, install the game, set up a shortcut; and ad the -console command line to the shortcut. It should look like: "C:\Program Files (x86)\Innonics\Diggles\Diggles.exe" -console in the Target text line.
Next, you can do two things here. You can either start the campaign, in which as soon as you can you should open the console with the ` key, and type in 'gamesave (save name)'. DO NOT USE THE SAVE GAME FEATURE IN THE MAIN MENU, IT WILL NOT WORK.
Now you can go back and exit the game, and we'll get on how to edit the .reg files. Start a search for the regedit system in Windows (If you're using anything else, I really cannot help you), and open it up. You'll find the Diggle files under HKEY_CURRENT_USER, then Software, then under SekOst (Or just run a search for SekOst).
Okay, strictly for the framerate, click the Performance table and you'll find a option that says MaxFramerate, with the data value set to 5. Just change that to whatever you're comfortable with. I use 60, myself.
From there you can close it out and start up the game again. You can either play a free-play mission, or go back to the campaign. From the Main Menu (DO NOT START A NEW GAME IN CAMPAIGN), open the console and type in 'gameload (save name)', and it'll load you right back to where you saved. That should fix your framerate problem.
UNDER NO CIRCUMSTANCES SHOULD YOU USE THE BUILT-IN SETTING EDITOR. IT DOES NOT WORK; AND IT'LL RESET YOUR REGRISTRY FILES.
For other features, like turning up animation and adding the partical effects, go back to the Performance tab in regedit and look for AnimInterpolation and Particles. Change both of those from 0 to 1.
To turn on or shut off MUSIC and SOUNDs, look in the Misc tab and turn them to 0 or 1, respectively.
To activate the game speed boost feature, go to Misc and set MaxGametimeFactor to something simple (I have it set to

, so that when you're playing you can press the + and - keys to increase and decrease the gamespeed. Normally you cannot continue playing like that, only watch, but if you set the NoGamespeedLock to 1 instead of 0, it'll aloow you to play, although you won't be able to see the gamespeed you're currenly running.
That usually isn't a problem, as if your diggles get into a fight or something, the game will automatically go back to the default speed and give you a big-oh warning.
If anyone has any other questions, let me know and I'll answer them to the best of my abilities.