Unfortunately you do not meet the minimum requirements to reliably play the game

FXIV: ARR Minimum System Requirements

Operating System: Windows® Vista 32/64bit, Windows® 7 32/64 bit
Processor: Intel® Core™2 Duo
Graphics: NVIDIA® Geforce® 8800 Series, ATI Radeon™ HD 4770
Memory: 2GB (4GB recommended for 64bit OS)
Disk Space: 20GB.

Taken directly from their website.