I installed Art Effect and it nags about no space on partition for 2466Mb swapfile. I tried lowering in the preferences to 512Mb: as a result it now nags about the fact that a swapfile should be bigger as my total amount of ram and after that it still complains that there is no space on the partition for 512Mb either.

So before I start fidling with all kinds of stuff and mess it all up .... maybe someone has the answer already ?

I have a swap file that goes from100 mb (min) to 664 mb (max) and this configuration gives no problem.
Of course, I'm using this values accorfing to hard disk space I can use but it's possible to cancel the swap file everytime Arteffect closes so to reset the space occupied by this file. Maybe you shouldn't set min/max values correctly since your disk space is not the problem for sure.