I wanted to load maximum 8 simultaniosly playing videos on GEM window, but the PD crashes and playback starts to slow down. Is there any method of preloading those videos into memory and then replacing them, so instead of 20 there would be only 8 of them loaded "in the system"? Maybe my hardware is limited for this kind of task?

please tell more about your config .

platform, hard disks, codec used etc..
the more the better

try first to encode to mjpeg (not mpeg) wich is light and uses intraframe compression.

@py
MacBook Pro, Intel Core 2 Duo 2,6 GHz, L2 Cache 6MB,
Memory 4 GB 667 MHz DDR2 SDRAM,
Bus Speed 800 MHz,
NVIDIA GeForce 8600M GT 512 MB

I will try the mjpeg.