Hello to Forum!
I have an Acer Aspire 5920G - 813G25Mi...
Specs:
CPU: Intel Core 2 Duo T8100 (2.1GHz) with 3MB L2 cache, at 800MHz
RAM: 3072MB (1 x 2048 and 1 x 1024) DDR2
HDD: 250GB SATA
Optical Drive: DVDRW double-layer drive
VGA Card: NVidia GeForce 8600M-GS (256MB)

Can I Install Snow Leopard or Leopard X on this and with which method???

Here is a video for you to look at:

YouTube - Mac OS X SNOW Leopard on Acer Aspire 5920G + Triple Boot Windows 7, Ubuntu, and Mac OS X

This guy includes links to the files that he used to get setup.

I have already seen this video... but there are some differences bettwen the specs:
[Acer Aspire 5920G Specs:
Processor: Intel Core 2 Duo T8300 2.4GHz (my: Intel Core 2 Duo T8100 2.1Ghz)
Chipset: Intel PM965
Platform: Intel Centrino Duo (Santa Rosa)
Memory: 4GB DDR2 667 High Performance Low Latency (my: 3GB DDR2)
Hard Drive: 250GB SATA 7200RPM
Video Card: NVIDIA GeForce 8600M GT 256MB (1024MB TurboCache) (my: NVidia GeForce 8600m gs 256mb)
Sound: Realtek High Definition ALC888
Screen: 15.4" Acer CrystalBrite LCD (aka. makeup mirror, waay too freaking reflective)
Optical: HD DVD (my dvd-multi)]

isn't that problem???

The processor is the same family, should be no problem. RAM does not matter. Video is same family...........I say give it a try, it might provide you with a good starting point. Although you might have issues with Ethernet and if your wireless is Intel 4965, it will not work. I tried to Hackintosh my own Acer 5920-6574 last year and I had problems with those items. I finally gave up when my nVidia card died (a known problem) and had to replace it with ATI mobile radeon (not supported).