Best flight sim games for my Mac system?

Here's my iMac info:
Mac OSX 10.4.11
Processor: 1.8 GHz PowerPC G5
Memory: 512 MB DDR SDRAM
Machine Name: iMac G5
Machine Model: PowerMac8,1
CPU Type: PowerPC G5 (3.0)
Bus Speed: 600 MHz
Built In Sound Card: Burr Brown PCM3052

Graphics:
GeForce FX 5200:
Chipset Model: GeForce FX 5200
VRAM (Total): 64 MB
Vendor: nVIDIA (0x10de)

Based on this system, what are the best flight sim games available for my Mac? Most of what I'm finding online needs more VRAM that I've got. Thanks.

If I wanted to increase my Video RAM, do I need to take in the computer to a Mac store, or can I do this at home?