It seems that a South African online retailer with a curious resemblance to the name of the publisher of San Andreas has put up system requirements for San Andreas PC.
It is not known whether these were provided by a source affiliated with Rockstar Games or the retailer in question, Take2.co.za, pulled the requirements out of the sky. Regardless, the requirements do look somewhat relevant.
Pentium PIII 800 MHz Processor or AMD Athlon
NVIDIA GeForce� or ATI Radeon� 7000 or higher
CDROM 4X or Faster
256 MB RAM
CPU Pentium 4 2.4GHz or Athlon 2200
Geforce FX 5700 or Radeon 9600 or higher
CDRom 52x or DVD Rom 16x
512 MB RAM
Unlike some german sites might lead you to believe, Take2.co.za is a retailer independent from the publisher of Grand Theft Auto: San Andreas, Take 2 Games. Keep in mind that these system requirements have not come directly from Rockstar Games and are therefore prone to change at any time.
Edit: Smoke from GTA Injection phoned the people at Take2.co.za up and it turns out the requirements are the assumptions of the retailer. So while they are not the final requirements, they are rather likely. Keep in mind that San Andreas might be shipping on a DVD disc, as is clued by the official boxart.