Sound card or Video card?

I have a P4 1.6 512 MB RAM (low-end by today's standards). My graphic card is the NVIDIA FX5200 and Soundblaster Live. My monitor refresh rate is 85 Hz. The only high-performance :) software I use is FS9. I listen to music and watch videos and surf the net occasionally on it, so it's fine for me.The problem I'm having is when I run FS9 and I switch views, I'll get a stuttering sound as the texture of the landscape and the plane load. If I go into SPOT view, it takes about 6-7 seconds on third-party planes (like the POSKY 757)and 2-4 seconds on the stock FS9 aircraft.The dillema that I have is that I can only afford to replace one item for now (sound card or video card). Which one should I replace first? I was thinking of getting the Sound Blaster Audigy 2 ZS Value and the ATI 9800 Pro.Thanks.